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# Previous year Questions (2016-20) - Vector Algebra and Three Dimensional Geometry Notes | EduRev

## Commerce : Previous year Questions (2016-20) - Vector Algebra and Three Dimensional Geometry Notes | EduRev

The document Previous year Questions (2016-20) - Vector Algebra and Three Dimensional Geometry Notes | EduRev is a part of the Commerce Course Mathematics (Maths) Class 12.
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Q.1. A vector  lies in the plane of the vectors  If  bisects the angle between  then    (2020)
(1)
(2)
(3)
(4)
Ans.
(3)
We have,

On comparing with
We get Î± = 4 and Î² = 4
Therefore,
Now, again consider

On comparing with we get

Therefore,

Q.2. Let  be three unit vectors such that  and  then the ordered pair,  is equal to    (2020)
(1)
(2)
(3)
(4)
Ans.
(4)
Given
...(1)
Taking square of both sides, we get

(since  are unit vectors)

Now,

Q.3. Let  be two vectors. If  is a vector such that  then  is equal to    (2020)
(1) -3/2
(2) 1/2
(3) -1/2
(4) -1
Ans.
(3)
Given

...(1)
Now,
and
Substituting these values in Eq. (1), we get

Hence,

Q.4. The projection of the line segment joining the points (1, âˆ’1, 3) and (2, âˆ’4, 11) on the line joining the points (âˆ’1, 2, 3) and (3, âˆ’2, 10) is _____.    (2020)
Ans.
(8.00)
We have

Hence, the required projection is

Q.5. If the vectors  are coplanar and  then the value of Î» is _____.    (2020)
Ans.
(1.00)
The vectors  are coplanar vectors, then

Therefore,  ...(1)
...(2)
...(3)
Now,  ...(4)

...(5)
Hence,

Q.6. Let  be three vectors such that  and the angle between  If  is perpendicular to the vector  is equal to ____.    (2020)
Ans.
(30.00)
Given,

Now,  is perpendicular to the vector  then
Hence,

Q.7. If the distance between the plane 23x - 10y - 2z + 48 =0 and the plane containing the lines  is equal to  then k is equal to _____.    (2020)
Ans.
(3.00)
The given lines must be intersecting

Therefore,
(2s - 1, 3s + 3, 8s - 1) = (2t - 3t, t - 2, Î»t + 1)
Now, 2s - 1 = 2t - 3 ...(1)
3s + 3 = t - 2 ...(2)
8s - 1 = Î»t + 1 ...(3)
On solving above equations, we get
t = -1, s = -2 and Î» = 18
Distance of plane contains given lines from given plane is same as distance between point (â€“3, â€“2, 1) from given plane. So,

Q.8. Let P be a plane passing through the points (2, 1, 0), (4, 1, 1) and (5, 0, 1) and R be any point (2, 1, 6). Then, the image of R in the plane P is    (2020)
(1) (6, 5, 2)
(2) (6, 5, âˆ’2)
(3) (4, 3, 2)
(4) (3, 4, âˆ’2)
Ans.
(2)
The equation of the plane passing through the points (2, 1, 0), (4, 1, 1) and (5, 0, 1) is

â‡’ (x - 2)(1) - (y - 1)(2 - 3) + z(-2) = 0
â‡’ x + y - 2z = 3

Let I and F are respectively image and foot of perpendicular of point R in the plane. So, the equation of RI is
(say)
â‡’ x = k + 2, y = k + 1 and z = -2k + 6
Hence, the coordinates of point F is
Point F lies in the plane, then

â‡’ 3k = 12 â‡’ k = 4
Hence, the image I is (6, 5, -2).

Q.9. If the foot of the perpendicular drawn from the point (1, 0, 3) on a line passing through (Î±, 7, 1) is   then Î± is equal to _____.
Ans.
(4.00)
We have,

Direction ratio of BP
Direction ratio of AP =
Since AP and BP are perpendicular, then

Q.10. The shortest distance between the lines  is    (2020)
(1) 2âˆš30
(2) 7/2 (âˆš30)
(3) 3âˆš30
(4) 3
Ans.
(3)
The equations of the lines are
...(1)
...(2)
The distance between the lines is given by

Now,

Hence,

Q.11. Let the volume of a parallelepiped whose coterminous edges are given by  and  be 1 cu. unit. If Î¸ be the angle between the edges  then cos Î¸ can be    (2020)
(1)
(2)
(3) 5/7
(4)
Ans.
(2)
The volume of parallelepiped is 1 cu. unit. Therefore,

â‡’ Î» = 2, 4
Now,

Q.12. The mirror image of the point (1, 2, 3) in a plane is  Which of the following points lies on this plane?    (2020)
(1) (1, 1, 1)
(2) (1, -1, 1)
(3) (-1, -1, 1)
(4) (-1, -1, -1)
Ans.
(2)
Direction ratios of normal to the plane is
<1 + (7/3), 2 + (4/3),3 + (1/3)> = <1, 1, 1>
The coordinates of mid- point of image and point is
The equation of plane is

â‡’ x + y + z = 1
Hence, the point (1, âˆ’1, 1) lies on the plane.

Q.13. If for some Î± and Î² in the intersection of the following three planes
x + 4y - 2z =1
x + 7y - 5z = Î²
x + 5y - Î±z = 5
is a line in then Î± + Î² is equal to    (2020)
(1) 0
(2) 10
(3) 2
(4) âˆ’10
Ans.
(2)
We have
=0
â‡’ (7Î± + 25) - (4Î± + 10) + (-20 + 14) = 0
â‡’ 3Î± + 9 = 0 â‡’ Î± = -3
and

Hence, Î± + Î² = -3 + 13 = 10

Q.14. Let  be a vector such that  then  is equal to:    (2019)
(1) 19/2
(2) 9
(3) 8
(4) 17/2
Ans.
(1)

Q.15. Let  and  be three vectors such that the projection vector of
If  is perpendicular to  is equal to:    (2019)
(1) âˆš32
(2) 6
(3) âˆš22
(4) 4
Ans.
(2)
Projection of
According to question
â‡’ b1 + b2 = 2    ...(1)
Since,  is perpendicular to
Hence
â‡’ 8 + 5b1 + b2 + 2 = 0 ...(2)
From (1) and (2),

Q.16. Let  and  be three vectors such that  and  is perpendicular to  Then a possible value of (Î»1, Î»2, Î»3) is:    (2019)
(1) (1, 3, 1)
(2) (-1/2, 4, 0)
(3) (1/2, 4, -2)
(4) (1, 5, 1)
Ans.
(2)

âˆ´ 3 - Î»2 = 2Î»1    ...(1)

...(2)
Since, (-1/2, 4, 0) satisfies equation (1) and (2). Hence, one of possible value of

Q.17. Let  be two given vectors where vectors are non-collinear. The value of Î» for which vectors  are collinear, is:    (2019)
(1) -4
(2) -3
(3) 4
(4) 3
Ans.
(1)
Let  are collinear for same k
i.e.,

But  are non-collinear, then

â‡’

Î» = -4

Q.18. Let and  be coplanar vectors. Then the non-zero vector is:    (2019)
(1)
(2)
(3)
(4)
Ans.
(4)
are coplanar

For (Rejected)

Q.19. Let  respectively be the position vectors of the points A, B and C with respect to the origin O. If the distance of C from the bisector of the acute angle between OA and OB is 3/âˆš2, then the sum of all possible values of Î² is:    (2019)
(1) 4
(2) 3
(3) 2
(4) 1
Ans.
(4)
Since, the angle bisector of acute angle between OA and OB would be y = x

Since, the distance of C from bisector = 3/âˆš2

Hence, the sum of all possible value of Î² = 2 + (-1) = 1

Q.20. The sum of the distinct real values of Î¼, for which the vectors,  are co-planar, is:    (2019)
(1) -1
(2) 0
(3) 1
(4) 2
Ans.
(1)
âˆµ Three vectors and  are copalnar.

Therefore, sum of all real values = 1 - 2 = -1

Q.21. Let  be three unit vectors, out of which vectors are non-parallel. If Î± and Î² are the angles which vector  makes with vectors  respectively and  then  is equal to:    (2019)
(1) 30Â°
(2) 90Â°
(3) 60Â°
(4) 45Â°
Ans.
(1)
Since,  are three unit vectors
âˆ´
Then,

âˆ´

â‡’ Î² = 60Â° and Î± = 90Â°
Hence,

Q.22. The magnitude of the projection of the vector  on the vector perpendicular to the plane containing the vectors  and  is:    (2019)
(1) âˆš3/2
(2) âˆš6
(3) 3âˆš6
(4)
Ans.
(4)
Let
âˆ´ Vector perpendicular to

Now, projection of vector  is

Q.23. Let  and  for some real x. Then  is possible if:    (2019)
(1)
(2)
(3)
(4)
Ans.
(2)
Given
Now,

Q.24. Let where  is parallel to is perpendicular to  then  is equal to:    (2019)
(1)
(2)
(3)
(4)
Ans.
(3)
...(1)
Since,  is perpendicular to

Cross product with  in equation (1)

Q.25. If a unit vector  makes angles Ï€/3 with  and Î¸ âˆˆ (0, Ï€) with  then a value of 0 is:    (2019)
(1) 5Ï€/6
(2) Ï€/4
(3) 5Ï€/12
(4) 2Ï€/3
Ans.
(4)
Let cos Î±, cos Î², cos Î³ be direction cosines of a.

Q.26. The distance of the point having position vector  from the straight line passing through the point (2, 3, -4) and parallel to the vector,  is:    (2019)
(1) 7
(2) 4âˆš3
(3) 6
(4) 2âˆš13
Ans.
(1)
Equation of the line is

Let the point M on the line l is (6Î» + 2, 3Î» + 3, -4Î» - 4)
Direction ratio's of PM is (6Î» + 3, 3Î» + 1, - 4Î»- 10)
â‡’ (6Î» + 3) (6) + (3Î» + 1) (3) + (-4Î».- 10) (- 4) = 0
â‡’ Î» = - 1 â‡’ M = (- 4, 0, 0)

Q.27. Let a = 3i + 2j + 2k and b = i + 2j - 2k be two vectors. If a vector perpendicular to both the vectors  has the magnitude 12 then one such vector is:    (2019)
(1)
(2)
(3)
(4)
Ans.
(2)
Let vector be

Given that magnitude of the vector is 12.

Q.28. Let Î± âˆˆ R and the three vectors  and  Then the set     (2019)
(1) is singleton
(2) is empty
(3) contains exactly two positive numbers
(4) contains exactly two numbers only one of which is positive
Ans.
(2)
Let, three vectors  are coplanar, then

âˆµ no real value of â€˜Î±â€™ exist,
âˆ´ set S is an empty set.

Q.29. The equation of the line passing through (-4, 3, 1), parallel to the plane x + 2y - z - 5 = 0 and intersecting the line is:    (2019)
(1)
(2)
(3)
(4)
Ans.
(3)
Let any point on the intersecting line

is (-3Î» - 1, 2Î» + 3, -Î» + 2)
Since, the above point lies on a line which passes through the point (-4, 3, 1)
Then, direction ratio of the required line

Since, line is parallel to the plane
x + 2y - z - 5 = 0
Then, perpendicular vector to the line is
Now (-3Î» + 3)(1) + (2Î»)(2) + (-Î» + 1)(-1) = 0
â‡’  Î» = - 1
Now direction ratio of the required line = <6, - 2, 2 > or <3,-1, 1>
Hence required equation of the line is

Q.30. The plane through the intersection of the planes x + y + z = 1 and 2x + 3y-z + 4 = 0 and parallel to j-axis also passes through the point:    (2019)
(1) (-3, 0, -1)
(2) (-3, 1, 1)
(3) (3, 3, -1)
(4) (3, 2, 1)
Ans.
(4)
Since, equation of plane through intersection of planes

But, the above plane is parallel to y-axis then

â‡’ Î» = -3
Hence, the equation of required plane is
-x - 4z + 7 = 0
â‡’ x + 4z - 7 = 0
Therefore, (3, 2, 1) the passes through the point.

Q.31. The equation of the plane containing the straight line  and perpendicular to the plane containing the straight lines  is:    (2019)
(1) x - 2y + z = 0
(2) 3x + 2y - 3z = 0
(3) x + 2y - 2z = 0
(4) 5x + 2y - 4z = 0
Ans.
(1)
Let the direction ratios of the plane containing lines

âˆ´ Direction ratio of plane = <-8, 1, 10>.
Let the direction ratio of required plane is <l, m, n>
Then-81 + m + 10n = 0    ...(1)
and 2l + 3m + 4n = 0    ...(2)
From (1) and (2),

âˆ´ D.R.s are <1, -2, 1>

âˆ´ Equation of plane: x - 2y + z = 0

Q.32. The plane passing through the point (4, -1, 2) and parallel to the lines  also passes through the point:    (2019)
(1) (1, 1, -1)
(2) (1, 1, 1)
(3) (-1, -1,-1)
(4) (-1, -1, 1)
Ans.
(2)
Equation of required plane is

(x - 4)(-3 -4) - (y + 1)(9 - 2) + (z - 2) (6 + 1) = 0

âˆµ point (1, 1, 1) satisfies this equation
âˆ´ point (1, 1, 1) lies on the plane

Q.33. Let A be a point on the line  and B(3, 2, 6) be a point in the space. Then the value of Î¼ for which the vector  is parallel to the plane x - 4y + 3z = 1 is:    (2019)
(1) 1/4
(2) 1/8
(3) 1/2
(4) -1/4
Ans.
(1)
âˆµ A be a point on given line.
âˆ´ Position vector of A

Equation of plane is: x - 4y + 3z = 1
âˆµ  is parallel to this plane.

â‡’ Î¼ = 1/4

Q.34. The plane which bisects the line segment joining the points (- 3, - 3, 4) and (3, 7, 6) at right angles, passes through which one of the following points?    (2019)
(1) (-2, 3, 5)
(2) (4, -1, 7)
(3) (2, 1, 3)
(4) (4, 1, -2)
Ans.
(4)

Q(0, 2, 5)
Since, direction ratios of normal to the plane is

Then, equation of the plane is
(x - 0)6 + (y - 2)10 + (z - 5)2 = 0
3x + 5y - 10 + z - 5 = 0
3x + 5y + z = 15    ...(1)
Since, plane (1) satisfies the point (4, 1, -2)
Hence, required point is (4, 1, -2)

Q.35. On which of the following lines lies the point of inter-section of the line, and the plane, x + y + z = 2?    (2019)
(1)
(2)
(3)
(4)
Ans.
(3)
Let any point on the line  be A(2Î» + 4, 2Î» + 5, Î», + 3) which lies on the plane x +y + z = 2
â‡’ 2Î» + 4 + 2Î» + 5 + Î» + 3 = 2
â‡’ 5Î» = -10 â‡’ Î» = - 2
Then, the point of intersection is (0, 1, 1)
which lies on the line

Q.36. The plane containing the line  and also containing its projection on the plane 2x + 3y- z = 5, contains which one of the following points?    (2019)
(1) (2, 2, 0)
(2) (-2, 2, 2)
(3) (0, -2, 2)
(4) (2, 0, -2)
Ans.
(4)
Let normal to the required plane is
â‡’  is perpendicular to both vector

â‡’ Equation of the required plane is
â‡’ (x - 3)(-8) + (y + 2) x 8 + (z - 1) x 8 = 0
â‡’ (x - 3) (-1) + (y + 2) x 1 + (z - 1) x 1 = 0
â‡’ x - 3 - y - 2 - z + 1 =0
âˆµ x - y - z = 4 passes through (2, 0, -2)
âˆ´ plane contains (2, 0, -2).

Q.37. The direction ratios of normal to the plane through the points (0, -1, 0) and (0,0, 1) and making an angle Ï€/4 with the plane y - z + 5 = 0 are:    (2019)
(1) 2, -1, 1
(2) 2, âˆš2, -âˆš2
(3) âˆš2, 1, -1
(4) 2âˆš3, 1, -1
Ans.
(2, 3)
Let the d.râ€™s of the normal be (a, b, c)
Equation of the plane is
a(x - 0) + b(y + 1) + c(z - 0) = 0
âˆµ It passes through (0, 0, 1)
âˆ´ b + c
Also

âˆ´ The d.râ€™s are âˆš2, 1, -1 or 2, âˆš2, -âˆš2

Q.38. Two lines  intersect at the point R. The reflection of R in the xy-plane has coordinates:    (2019)
(1) (2, -4, -7)
(2) (2, 4, 7)
(3) (2, -4, 7)
(4) (-2, 4, 7)
Ans.
(1)
Let the coordinate of P with respect to line

and coordinate of P w.r.t.

From above equation : Î» = -1, Î¼ = 1 .
âˆ´ Coordinate of point of intersection R = (2, -4, 1).
Image of R w.r.t. xy plane = (2, -4, -7).

Q.39. If the point (2, Î±, Î²) lies on the plane which passes through the points (3,4, 2) and (7, 0, 6) and is perpendicular to the plane 2x-5y = 15, then 2Î± - 3Î² is equal to:    (2019)
(1) 12
(2) 7
(3) 5
(4) 17
Ans.
(2)
Let the normal to the required plane is n, then

âˆ´ Equation of the plane
(x - 3) x 20 + (y - 4) x 8 + (z - 2) x (-12) = 0
5x - 15 + 2y - 8 - 3z + 6 = 0
5x + 2y - 3z - 17 = 0    ...(1)
Since, equation of plane (1) passes through (2, Î±, Î²), then

Q.40. The perpendicular distance from the origin to the plane containing the two lines,  and  is:    (2019)
(1) 11âˆš6
(2) 11/âˆš6
(3) 11
(4) 6/âˆš11
Ans.
(2)
âˆµ plane containing both lines.
âˆ´ D.R. of plane
Now, equation of plane is,
7(x - 1) - 14(y - 4) + 7 (z + 4) = 0
â‡’ x - 1 - 2y + 8 + z + 4 = 0
â‡’ x - 2y + z + 11 = 0
Hence, distance from (0, 0, 0) to the plane,

Q.41. If an angle between the line,  and the plane, x - 2y - kx = 3 is  then a value of k is    (2019)
(1)
(2)
(3) -3/5
(4) -5/3
Ans.
(1)
Let angle between line and plane is Î¸, then

Since,
Then,

Q.42. Let S be the set of all real values of Î» such that a plane passing through the points {-Î»2, 1, 1), (1, -Î»2, 1) and (1, 1, -Î»2) also passes through the point-(-1,-1, 1). Then S is equal to:    (2019)
(1) {âˆš3}
(2) {âˆš3, -âˆš3}
(3) {1, -1}
(4) {3, -3}
Ans.
(2)
Let  D(-1, -1, 1) lie on same plane, then

â‡’ (Î»2 + 1)((1 -Î»2)-4) = 0
â‡’ (3 - Î»2)(Î»+ 1) = 0 â‡’ Î»2 = 3

Hence, S = {-âˆš3, âˆš3}

Q.43. The equation of a plane containing the line of intersection of the planes 2x - y - 4 = 0 and y + 2z - 4 = 0 and passing through the point (1, 1, 0) is:    (2019)
(1) x- 3y- 2z = -2
(2) 2x - z = 2
(3) x - y - z = 0
(4) x + 3y + z = 4
Ans.
(3)
Let the equation of required plane be;
(2x - y - 4) + Î»(y + 2z - 4) = 0
âˆ´  This plane passes through the point (1, 1, 0) then (2 - 1 - 4) + Î»(1 + 0 - 4) = 0
â‡’ Î» = -1
Then, equation of required plane is,
(2x - y - 4) - (y + 2z - 4) = 0
â‡’ 2x - 2y â€” 2z = 0 â‡’ x - y - z = 0

Q.44. The length of the perpendicular from the point (2, -1, 4) on the straight line, is:    (2019)
(1) greater than 3 but less than 4
(2) less than 2
(3) greater than 2 but less than 3
(4) greater than 4
Ans.
(1)
Let P be the foot of perpendicular from point T (2, -1, 4) on the given line. So P can be assumed as P(10Î» - 3, -7Î» + 2, Î»)

DR's of TP is proportional to 10Î» - 5, - 7Î» + 3, Î» - 4
âˆµ TP and given line are perpendicular, so
10(10Î» - 5) -7 (- 7Î» + 3)+ 1(Î» - 4) = 0

Hence, the length of perpendicular is greater than 3 but less than 4.

Q.45. The vector equation of the plane through the line of intersection of the planes x + y + z = 1 and 2x + 3y + 4z = 5 which is perpendicular to the plane x - y + z = 0 is:    (2019)
(1)
(2)
(3)
(4)
Ans.
(4)
Equation of the plane passing through the line of intersection of x + y + z = 1 and 2x + 3y + 4z = 5 is (2x + 3y + 4z - 5) + Î» (x + y + z - 1) = 0
âˆµ plane (i) is perpendicular to the plane x-y + z = 0
âˆ´ (2 + Î»)(1) + (3 + Î»)(- 1) + (4 + Î»)(1) = 0
2 + Î» - 3 - Î» + 4 + Î» = 0
â‡’ Î» = -3
Hence, equation of required plane is -x + z- 2 = 0 or x - z + 2 = 0

Q.46. If a point R(4, y, z) lies on the line segment joining the points P(2, -3, 4) and Q(8, 0, 10), then distance of R from the origin is:    (2019)
(1) 2âˆš14
(2) 2âˆš21
(3) 6
(4) âˆš53
Ans.
(1)
Here, P, Q, R are collinear

Now, or =

Q.47. If the line,  meets the plane, x + 2y + 3z = 15 at a point P, then the distance of P from the origin is:    (2019)
(1) âˆš5 / 2
(2) 2 / âˆš5
(3) 9/2
(4) 7/2
Ans.
(3)
Let point on line be P (2k + 1, 3k - 1, 4k + 2)
Since, point P lies on the plane x + 2y + 3z = 15
âˆ´ 2k + 1 + 6k - 2 + 12k + 6= 15
â‡’ k = 1/2

Then the distance of the point P from the origin is

Q.48. A plane passing through the points (0, -1, 0) and (0, 0, 1) and making an angle Ï€/4 with the plane y - z + 5 = 0, also passes through the point:    (2019)
(1) (-âˆš2, 1, -4)
(2) (-âˆš2, -1, 4)
(3) (-âˆš2, -1, -4)
(4) (âˆš2, 1, 4)
Ans.
(4)
Let the required plane passing through the points (0,-1, 0) and (0, 0, 1) be  and the given plane is y - z + 5 = 0

Then, the equation of plane is

Then the point (âˆš2, 1, 4) satisfies the equation of plane -âˆš2x - y + z = 1

Q.49. The vertices B and C of a Î”ABC lie on the line,  such that BC = 5 units. Then the area (in sq. units) of this triangle, given that the point A (1, -1, 2), is:    (2019)
(1) 5âˆš17
(2) 2âˆš34
(3) 6
(4) âˆš34
Ans.
(4)
Let a point D on BC = (3Î» - 2, 1, 4Î»)

Hence,

Area of triangle

Q.50. Let P be the plane, which contains the line of intersection of the planes, x + y + z - 6 = 0 and 2x + 3y + z + 5 = 0 and it is perpendicular to the xy-plane. Then the distance of the point (0, 0, 256) from P is equal to:    (2019)
(1) 17/âˆš5
(2) 63âˆš5
(3) 205âˆš5
(4) 11/âˆš5
Ans.
(4)
Let the plane be
P = (2x + 3y + z + 5) + Î»(x: +y + z- 6) = 0
âˆµ above plane is perpendicular to xy plane.

Hence, the equation of the plane is,
P = x + 2y+ 11 = 0
Distance of the plane P from (0, 0, 256)

Q.51. If Q (0, -1, -3) is the image of the point P in the plane 3x - y + 4z = 2 and R is the point (3, -1, -2), then the area (in sq. units) of Î”PQR is:    (2019)
(1) 2âˆš13
(2) âˆš91/4
(3) âˆš91/2
(4) âˆš65/2
Ans.
(3)
Image of Q (0, -1, -3) in plane is,

Q.52. Let A(3, 0, -1), B(2, 10, 6) and C (1, 2, 1) be the vertices of a triangle and M be the midpoint of AC. If G divides BM in the ratio, 2 : 1, then cos (âˆ GOA)(O being the origin) is equal to:    (2019)
(1)
(2) 1/âˆš15
(3)
(4) 1/âˆš30
Ans.
(2)
G is the centroid of Î”ABC.

Q.53. If the length of the perpendicular from the point (Î², 0, Î²) (Î² â‰  0) to the line,  then Î² is equal to:    (2019)
(1) 1
(2) 2
(3) -1
(4) -2
Ans.
(3)
Given,  (let) and point P (Î², 0, Î²)
Any point on line A = (p, 1, -p -1)
Now, DR of AP â‰¡ <p - Î², 1 - 0 - p - 1 - Î²>
Which is perpendicular to line.

Given that distance AP

âˆ´ Î² = -1

Q.54. A perpendicular is drawn from a point on the line  to the plane x + y + z = 3 such that the foot of the perpendicular Q also lies on the plane x - y + z = 3. Then the co-ordinates of Q are:    (2019)
(1) (1, 0, 2)
(2) (2, 0, 1)
(3) (-1, 0, 4)
(4) (4, 0, -1)
Ans.
(2)

Let co-ordinates of Q be (Î±, Î², Î³), then
Î± + Î² + Î³ = 3    ...(i)
Î± - Î² + Î³ = 3    ...(ii)
â‡’ Î± + Î³ = 3 and Î² = 0
Equating direction ratio's of PQ, we get

Substituting the values of a and y in equation (i), we get
â‡’ 5Î» + 3 = 3 â‡’ Î» = 0
Hence, point is Q (2, 0, 1)

Q.55. If the plane 2x - y + 2z + 3 =0 has the distances 1/2 and 2/3 units from the planes 4x - 2y + 4z + Î» = 0 and 2x - y + 2z + Î¼ = 0, respectively, then the maximum value of Î» + Î¼ is equal to:    (2019)
(1) 9
(2) 15
(3) 5
(4) 13
Ans.
(4)
Let,

Given, distance between P1 and P2 is 1/3

And distance between P1 and P3 is 2/3

Q.56. If the line  intersects the plane 2x + 3y - z + 13 = 0 at a point P and the plane 3x + y + 4z = 16 at a point Q, then PQ is equal to:    (2019)
(1) 14
(2) âˆš14
(3) 2âˆš7
(4) 2âˆš14
Ans.
(4)
Let points P (3Î» + 2, 2Î» - 1, - Î» + 1) and Q(3Î¼ + 2, 2Î¼ - 1, - Î¼ + 1)

Hence, P (- 1, -3, 2)
Similarly, Q lies on 3x + y + 4z = 16

Hence, Q is (5, 1, 0)

Q.57. A plane which bisects the angle between the two given planes 2x - y + 2z -4 = 0 and x + 2y + 2z - 2 = 0, passes through the point:    (2019)
(1) (-1, -4, 1)
(2) (1, 4, -1)
(3) (2, 4, 1)
(4) (2, -4, 1)
Ans.
(4)
The equations of angle bisectors are,

â‡’ x - 3y - 2 = 0
or 3x + y + 4z - 6 = 0
(2, -4, 1) lies on the second plane.

Q.58. The length of the perpendicular drawn from the point (2, 1,4) to the plane containing the lines  is:    (2019)
(1) 3
(2) 1/3
(3) âˆš3
(4) 1/âˆš3
Ans.
(3)
The equation of plane containing two given lines is,

On expanding, we get x - y - z = 0
Now, the length of perpendicular from (2, 1, 4) to this plane

Q.59. Let be a vector coplanar with the vectors  and  perpendicular to  then, is equal to:    (2018)
(1) 336
(2) 315
(3) 256
(4) 84
Ans.
(1)

Q.60. If L1 is the line of intersect ion of the planes  2x - 2y + 3z = 0, x - y + z = 0 and L2 is the line of intersection of the planes x + 2y - z - 3 = 0, 3x - y + 2z = 0 then the distance of the origin fro m the plane, containing the lane L1 and L2 , is:    (2018)

(1)
(2)
(3)
(4)
Ans.
(2)
Vectors along the given lines L1, L2 are

and
Putting y = 0 in 1st two equation

Point on the plane is (â€“5, 0, 4) and normal vector of required plane is

Hence, equation of plane is - 7x + 7y - 8z - 3 = 0
Perpendicular distance is

Q.61. The length of the project ion of the line segment joining the points (5, -1, 4) and (4, -1, 3) on the plane, x + y + z = 7 is:    (2018)
(1) 2/âˆš3
(2) 2/3
(3) 1/3
(4)
Ans.
(4)
D.Râ€™s of AB = (1, 0, 1)
D.Râ€™s of normal to plane = (1, 1, 1)

AB = âˆš2

Length of projection =

Q.62. Let  and be a vector such that  and the angle between be 30Â°. Then is equal to    (2017)
(1) 1/8
(2) 25/8
(3) 2
(4) 5
Ans.
(3)

Q.63. If the image of the point P(1, â€“2, 3) in the plane, 2x + 3y â€“ 4z + 22 = 0 measured parallel to the line, x/1 = y/4 = z/5 is Q, then PQ is equal to    (2017)
(1) 6âˆš5
(2) 3âˆš5
(3) 2âˆš42
(4) âˆš42
Ans.
(3)
Equation of PQ,

Let M be (Î»+1, 4Î»- 2, 5Î»+ 3)

As it lies on 2x + 3y â€“ 4z + 22 = 0
Î» = 1
For Q, Î» = 2
Distance PQ

Q.64. The distance of the point (1, 3, â€“7) from the plane passing through the point (1, â€“1, â€“1), having normal perpendicular to both the lines  and  is     (2017)
(1) 10/âˆš74
(2) 20/âˆš74
(3) 10/âˆš83
(4) 5/âˆš83
Ans.
(3)
Let the plane be
a(x - 1)+ b( y + 1) + c(z +1) = 0
It is perpendicular to the given lines
a â€“ 2b + 3c = 0
Solving, a : b : c = 5 : 7 : 3
âˆ´ The plane is 5x + 7y + 3z + 5 = 0
Distance of (1, 3, â€“7) from this plane = 10/âˆš83

Q.65. The coodinates of the foot of the perpendicular from the point (1, -2,1) on the plane containing the lines,  and  is:    (2017)
(1) (2, -4, 2)
(2) (1, 1, 1)
(3) (0, 0, 0)
(4) (-1, 2, -`= 1)
Ans.
(3)

Q.66. The line of intersection of the planes  and  is:    (2017)
(1)
(2)
(3)
(4)
Ans.
(3)

13 x = 6
x = 6/13y
y = 5/13
.... is

Q.67. The area (in sq. units) of the parallelogram whosed diagonals are along the vectors  and  is:    (2017)
(1) 20
(2) 65
(3) 52
(4) 26
Ans.
(2)

Q.68. If the line,  lies in the plane, 2x - 4y + 3z = 2, then the shortest distance between this line and the line,  is:    (2017)
(1) 1
(2) 2
(3) 3
(4) 0
Ans.
(4)
pt (3, -2, Î») on pline 2x - 4y +3z - 2 = 0
= 6 + 8 - 3Î» - 2 = 0

Now
...(1)
...(2)

p (1, 0, 0)
gives are ditersech - thortest distance = 0

Q.69. If x = a,  y = b, z = c is a solution of the system of linear equations
x + 8y + 7z = 0
9x + 2y +3z = 0
y + y + z = 0
such that the point (a, b, c) lies on the plane x + 2y + z = 6, then 2a + b + c equals:    (2017)
(1) 2
(2) -1
(3) 1
(4) 0
Ans.
(1)

Q.70. If the vector is written as the sum of a vector  parallel to  and a vector  perpendicular to  is equal to:    (2017)
(1)
(2)
(3)
(4)
Ans.
(1)

Q.71. If a variable plane, at a distance of 3 units from the origin, intersects the coordinate axes at A, B and C, then the locus of the centroid of Î”ABC is.    (2017)
(1)
(2)
(3)
(4)
Ans.
(1)
Let Centroid be (h, k, l)
âˆ´ x - intp = 3h Y - intp = 3k, 3 - int = 3l

Q.72. The distance of the point (1, -5, 9) from the plane x - y + z = 5 measured along the line x = y = z is:    (2016)
(1) 3âˆš10
(2) 10âˆš3
(3) 10/âˆš3
(4) 20/3
Ans.
(2)
Let Q(1, -5, 9)

Line is (say)
Any pt on line we can take P(r + 1, r - 5, r + 9)
So, Pt satisfy Plane
=>(r + 1) - (r - 5) + (r + 9) = 5 r = -10 So, Point P = (-9, -15, -1)
Distance is PQ =

Q.73. If the line,  lies in the plane, lx + my - z = 9, then l2 + m2 is equal to:    (2016)
(1) 26
(2) 18
(3) 5
(4) 24
Ans. (4)
Point on line is P = (3, -2, -4)
'Pâ€™ lies on lx + my - z = 9
=> 3l - 2m + 4  = 9
3l - 2m = 5 ....(1)
As line lies on plane
=> 2 x l + m x (-1) + 3 x (-1) = 0
2l - m = 3 .....(3)
Solving l = 1, m = -1
So, l+ m= 2

Q.74. Let andbe three unit vectors such that If is not parallel to c , then the angle betweenandis:    (2016)
(1) 3Ï€/4
(2) Ï€/2
(3) 2Ï€/3
(4) 5Ï€/6
Ans.
(4)

Equate,

as unit vectors

Q.75. The shortest distance between the lines  and  lies in the interval:    (2016)
(1) (2, 3]
(2) [0, 1)
(3) (3, 4]
(4) [1, 2)
Ans.
(1)

Q.76. The distance of the point (1, -2, 4) from the plane passing through the point (1, 2, 2) and perpendicular to the planes x - y + 2z = 3 and 2x - 2y + z + 12 = 0, is   (2016)
(1) 1/âˆš2
(2) 2
(3) âˆš2
(4) 2âˆš2
Ans.
(4)
Equation of plane âŠ¥ to the planes.
x - y + 2z = 3 & 2x - 2y + z + 12 = 0
and passes through (1, 2, 2) is

3(x - 1) + 3(y - 2) = 0
x + y = 3 ..... (1)
distance of plane x + y - 3 = 0 from (1, - 2, 4) is

Q.77. In a triangle ABC, right angled at the vertex A, if the position vectors of A, B and C are respectively  and  then the point (p, q) lies on a line    (2016)
(1) parallel to y-axis
(2) making an acute angle with the positive direction of x-axis
(3) parallel to x-axis
(4) making an obtuse angle with the position direction of x-axis.
Ans.
(2)

â‡’ - 8 + 2(9 - 1) - 3 (p + 1) = 0 â‡’ - 3p + 2q - 13 = 0
â‡’ (p, q) lies on line
3x - 2y + 13 = 0
slope = 3/2

Q.78. ABC is a triangle in a plane with vertices A(2, 3, 5), B(-1, 3, 2) and C(Î», 5, Âµ). If the median through A is equally inclined to the coordinate axes, then the value of (Î»3 + Âµ3  + 5) is    (2016)
(1) 676
(2) 1130
(3) 1348
(4) 1077
Ans.
(3)

â‡’

Q.79. Let ABC be a triangle whose circumcentre is at P. If the position vectors of A, B, C and P are  and  respectively, then the position vector of the orthocentre of this triangle, is    (2016)
(1)
(2)
(3)
(4)
Ans.
(4)
Position vector of the centroid of
Now we known that centroid divides the line joining orthocentre to circum centre divided by centriod divided by centroid in the ratio in 2 : 1

Q.80. The number of distinct real values of Î» for which the lines  are coplanar is    (2016)
(1) 3
(2) 2
(3) 1
(4) 4
Ans.
(1)

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## Mathematics (Maths) Class 12

209 videos|222 docs|124 tests

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