Page 1
JEE Mains Previous Year Questions
(2021-2024): Vector Algebra
2024
Q1: Let ??? = -?? ??ˆ + ??ˆ - ?? ?? ˆ
,??
= ??ˆ + ?? ??ˆ - ?? ?? ˆ
and
?? = ( ( ??? × ??
)× ??ˆ)× ??ˆ)× ??ˆ. Then ??? · ( -??ˆ + ??ˆ + ?? ˆ
) is equal to :
(A) -12
(B) -10
(C) -13
(D) -15 [JEE Main 2024 (Online) 1st February Morning Shift]
Ans: (a)
?? = -5 · ??ˆ + ??ˆ - 3?? ˆ
,?? ?
= ??ˆ + 2??ˆ - 4?? ˆ
?? = ( ( ( ?? × ?? ?
)× ??ˆ)× ??ˆ)× ??ˆ
= ( ( ( ?? · ??ˆ) ?? ?
- ( ?? ?
· ??ˆ) ?? )× ??ˆ)× ??ˆ
= ( ( -5?? ?
- ?? )× ??ˆ)× ??ˆ
= ( ( -11??ˆ + 23?? ˆ
)× ??ˆ)× ??ˆ
= ( 11?? ˆ
+ 23??ˆ)× ??ˆ
= ( 11??ˆ - 23?? ˆ
)
?? · ( -??ˆ + ??ˆ + ?? ˆ
)= 0 + 11- 23
= -12
Q2: Let ??? ? = ?? ??ˆ + ??ˆ - ?? ?? ˆ
,?? ? ?
= ?? ??ˆ + ??ˆ + ?? ?? ˆ
and ??? = ??ˆ - ?? ??ˆ + ?? ?? ˆ
be three vectors. If a vectors ??? ?
satisfies ??? ? × ?? ? ?
= ??? × ?? ? ?
and ??? ? · ??? ? = ?? , then ??? ? · ( ??ˆ - ??ˆ - ?? ˆ
) is equal to
(A)24
(B) 32
(C) 36
(D )28 [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (b)
?? × ?? ?
- ?? × ?? ?
= 0
?
( ?? - ?? )× ?? ?
= 0
?
?? - ?? = ?? ?? ?
? ?? = ?? + ?? ?? ?
Now, p ? · a ? = 0 (given)
Page 2
JEE Mains Previous Year Questions
(2021-2024): Vector Algebra
2024
Q1: Let ??? = -?? ??ˆ + ??ˆ - ?? ?? ˆ
,??
= ??ˆ + ?? ??ˆ - ?? ?? ˆ
and
?? = ( ( ??? × ??
)× ??ˆ)× ??ˆ)× ??ˆ. Then ??? · ( -??ˆ + ??ˆ + ?? ˆ
) is equal to :
(A) -12
(B) -10
(C) -13
(D) -15 [JEE Main 2024 (Online) 1st February Morning Shift]
Ans: (a)
?? = -5 · ??ˆ + ??ˆ - 3?? ˆ
,?? ?
= ??ˆ + 2??ˆ - 4?? ˆ
?? = ( ( ( ?? × ?? ?
)× ??ˆ)× ??ˆ)× ??ˆ
= ( ( ( ?? · ??ˆ) ?? ?
- ( ?? ?
· ??ˆ) ?? )× ??ˆ)× ??ˆ
= ( ( -5?? ?
- ?? )× ??ˆ)× ??ˆ
= ( ( -11??ˆ + 23?? ˆ
)× ??ˆ)× ??ˆ
= ( 11?? ˆ
+ 23??ˆ)× ??ˆ
= ( 11??ˆ - 23?? ˆ
)
?? · ( -??ˆ + ??ˆ + ?? ˆ
)= 0 + 11- 23
= -12
Q2: Let ??? ? = ?? ??ˆ + ??ˆ - ?? ?? ˆ
,?? ? ?
= ?? ??ˆ + ??ˆ + ?? ?? ˆ
and ??? = ??ˆ - ?? ??ˆ + ?? ?? ˆ
be three vectors. If a vectors ??? ?
satisfies ??? ? × ?? ? ?
= ??? × ?? ? ?
and ??? ? · ??? ? = ?? , then ??? ? · ( ??ˆ - ??ˆ - ?? ˆ
) is equal to
(A)24
(B) 32
(C) 36
(D )28 [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (b)
?? × ?? ?
- ?? × ?? ?
= 0
?
( ?? - ?? )× ?? ?
= 0
?
?? - ?? = ?? ?? ?
? ?? = ?? + ?? ?? ?
Now, p ? · a ? = 0 (given)
So, c · a ? + ?? a ? · b
?
= 0
( 3 - 3 - 8)+ ?? ( 12+ 1 - 14)= 0
?? = -8
p ? = c - 8b
?
p ? = -31i ˆ - 11j ˆ - 52k
ˆ
So, p ? · ( i ˆ - j ˆ - k
ˆ
)
= -31+ 11+ 52
= 32
Q3: The distance of the point ?? ( ?? ,?? ,-?? ) form the line passing through the point ?? ( ?? ,-?? ,?? ) and
perpendicular to the lines ??? = ( -?? ??ˆ + ?? ?? ˆ
)+ ?? ( ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
) ,?? ? R and ??? = ( ??ˆ - ?? ??ˆ + ?? ˆ
)+ ?? ( -??ˆ +
?? ??ˆ + ?? ?? ˆ
) ,?? ? R is :
(A) v????
(B) v????
(C) v????
(D) v???? [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (a)
A vector in the direction of the required line can be obtained by cross product of
|
??ˆ ??ˆ ?? ˆ
2 3 5
-1 3 2
|
= -9??ˆ - 9??ˆ + 9?? ˆ
Required line
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? '
( -9i ˆ - 9j ˆ + 9k
ˆ
)
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? ( i ˆ + j ˆ - k
ˆ
)
Now distance of ( 0,2,-2)
Page 3
JEE Mains Previous Year Questions
(2021-2024): Vector Algebra
2024
Q1: Let ??? = -?? ??ˆ + ??ˆ - ?? ?? ˆ
,??
= ??ˆ + ?? ??ˆ - ?? ?? ˆ
and
?? = ( ( ??? × ??
)× ??ˆ)× ??ˆ)× ??ˆ. Then ??? · ( -??ˆ + ??ˆ + ?? ˆ
) is equal to :
(A) -12
(B) -10
(C) -13
(D) -15 [JEE Main 2024 (Online) 1st February Morning Shift]
Ans: (a)
?? = -5 · ??ˆ + ??ˆ - 3?? ˆ
,?? ?
= ??ˆ + 2??ˆ - 4?? ˆ
?? = ( ( ( ?? × ?? ?
)× ??ˆ)× ??ˆ)× ??ˆ
= ( ( ( ?? · ??ˆ) ?? ?
- ( ?? ?
· ??ˆ) ?? )× ??ˆ)× ??ˆ
= ( ( -5?? ?
- ?? )× ??ˆ)× ??ˆ
= ( ( -11??ˆ + 23?? ˆ
)× ??ˆ)× ??ˆ
= ( 11?? ˆ
+ 23??ˆ)× ??ˆ
= ( 11??ˆ - 23?? ˆ
)
?? · ( -??ˆ + ??ˆ + ?? ˆ
)= 0 + 11- 23
= -12
Q2: Let ??? ? = ?? ??ˆ + ??ˆ - ?? ?? ˆ
,?? ? ?
= ?? ??ˆ + ??ˆ + ?? ?? ˆ
and ??? = ??ˆ - ?? ??ˆ + ?? ?? ˆ
be three vectors. If a vectors ??? ?
satisfies ??? ? × ?? ? ?
= ??? × ?? ? ?
and ??? ? · ??? ? = ?? , then ??? ? · ( ??ˆ - ??ˆ - ?? ˆ
) is equal to
(A)24
(B) 32
(C) 36
(D )28 [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (b)
?? × ?? ?
- ?? × ?? ?
= 0
?
( ?? - ?? )× ?? ?
= 0
?
?? - ?? = ?? ?? ?
? ?? = ?? + ?? ?? ?
Now, p ? · a ? = 0 (given)
So, c · a ? + ?? a ? · b
?
= 0
( 3 - 3 - 8)+ ?? ( 12+ 1 - 14)= 0
?? = -8
p ? = c - 8b
?
p ? = -31i ˆ - 11j ˆ - 52k
ˆ
So, p ? · ( i ˆ - j ˆ - k
ˆ
)
= -31+ 11+ 52
= 32
Q3: The distance of the point ?? ( ?? ,?? ,-?? ) form the line passing through the point ?? ( ?? ,-?? ,?? ) and
perpendicular to the lines ??? = ( -?? ??ˆ + ?? ?? ˆ
)+ ?? ( ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
) ,?? ? R and ??? = ( ??ˆ - ?? ??ˆ + ?? ˆ
)+ ?? ( -??ˆ +
?? ??ˆ + ?? ?? ˆ
) ,?? ? R is :
(A) v????
(B) v????
(C) v????
(D) v???? [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (a)
A vector in the direction of the required line can be obtained by cross product of
|
??ˆ ??ˆ ?? ˆ
2 3 5
-1 3 2
|
= -9??ˆ - 9??ˆ + 9?? ˆ
Required line
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? '
( -9i ˆ - 9j ˆ + 9k
ˆ
)
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? ( i ˆ + j ˆ - k
ˆ
)
Now distance of ( 0,2,-2)
P.V. of P = ( 5 + ?? ) ??ˆ + ( ?? - 4) ??ˆ + ( 3 - ?? ) ?? ˆ
AP
?????
= ( 5 + ?? ) ??ˆ + ( ?? - 6) ??ˆ + ( 5 - ?? ) ?? ˆ
AP
?????
· ( i ˆ + j ˆ - k
ˆ
)= 0
5 + ?? + ?? - 6 - 5 + ?? = 0
?? = 2
|AP
?????
| = v49 + 16 + 9
|AP
?????
| = v74
Q4: Let ?? ?? :??? = ( ??ˆ - ??ˆ + ?? ?? ˆ
)+ ?? ( ??ˆ - ??ˆ + ?? ?? ˆ
) ,?? ? R,
?? ?? :??? = ( ??ˆ - ?? ˆ
)+ ?? ( ?? ??ˆ + ??ˆ + ?? ?? ˆ
) ,?? ? R, and ?? ?? :??? = ?? ( ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
) ,?? ? R
be three lines such that ?? ?? is perpendicular to ?? ?? and ?? ?? is perpendicular to both ?? ?? and ?? ?? . Then, the
point which lies on ?? ?? is
(A) ( ?? ,?? ,-?? )
(B) ( ?? ,-?? ,?? )
(C) ( -?? ,?? ,?? )
(D) ( -,?? - ?? ,?? ) [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (c)
L
1
? L
2
L
3
? L
1
, L
2
3 - 1 + 2P = 0
P = -1
|
i ˆ j ˆ k
ˆ
1 -1 2
3 1 -1
| = -i ˆ + 7j ˆ + 4k
ˆ
? ( -?? ,7?? ,4?? ) will lie on L
3
For ?? = 1 the point will be ( -1,7,4)
Q5: Let ??? ? = ??ˆ + ?? ??ˆ + ?? ?? ˆ
,?? ,?? ? R. Let a vector ?? ? ?
be such that the angle between ??? ? and ?? ? ?
is
?? ?? and
|?? ? ?
|
?? = ?? . If ??? ? · ?? ? ?
= ?? v?? , then the value of ( ?? ?? + ?? ?? ) |??? ? × ?? ? ?
|
?? is equal to
A. 85
B. 90
C. 75
D. 95 [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (b)
|b
?
|
2
= 6;|a ? ||b
?
|cos ?? = 3v2
|a ? |
2
|b
?
|
2
cos
2
?? = 18
|a ? |
2
= 6
Also 1 + ?? 2
+ ?? 2
= 6
?? 2
+ ?? 2
= 5
to find
Page 4
JEE Mains Previous Year Questions
(2021-2024): Vector Algebra
2024
Q1: Let ??? = -?? ??ˆ + ??ˆ - ?? ?? ˆ
,??
= ??ˆ + ?? ??ˆ - ?? ?? ˆ
and
?? = ( ( ??? × ??
)× ??ˆ)× ??ˆ)× ??ˆ. Then ??? · ( -??ˆ + ??ˆ + ?? ˆ
) is equal to :
(A) -12
(B) -10
(C) -13
(D) -15 [JEE Main 2024 (Online) 1st February Morning Shift]
Ans: (a)
?? = -5 · ??ˆ + ??ˆ - 3?? ˆ
,?? ?
= ??ˆ + 2??ˆ - 4?? ˆ
?? = ( ( ( ?? × ?? ?
)× ??ˆ)× ??ˆ)× ??ˆ
= ( ( ( ?? · ??ˆ) ?? ?
- ( ?? ?
· ??ˆ) ?? )× ??ˆ)× ??ˆ
= ( ( -5?? ?
- ?? )× ??ˆ)× ??ˆ
= ( ( -11??ˆ + 23?? ˆ
)× ??ˆ)× ??ˆ
= ( 11?? ˆ
+ 23??ˆ)× ??ˆ
= ( 11??ˆ - 23?? ˆ
)
?? · ( -??ˆ + ??ˆ + ?? ˆ
)= 0 + 11- 23
= -12
Q2: Let ??? ? = ?? ??ˆ + ??ˆ - ?? ?? ˆ
,?? ? ?
= ?? ??ˆ + ??ˆ + ?? ?? ˆ
and ??? = ??ˆ - ?? ??ˆ + ?? ?? ˆ
be three vectors. If a vectors ??? ?
satisfies ??? ? × ?? ? ?
= ??? × ?? ? ?
and ??? ? · ??? ? = ?? , then ??? ? · ( ??ˆ - ??ˆ - ?? ˆ
) is equal to
(A)24
(B) 32
(C) 36
(D )28 [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (b)
?? × ?? ?
- ?? × ?? ?
= 0
?
( ?? - ?? )× ?? ?
= 0
?
?? - ?? = ?? ?? ?
? ?? = ?? + ?? ?? ?
Now, p ? · a ? = 0 (given)
So, c · a ? + ?? a ? · b
?
= 0
( 3 - 3 - 8)+ ?? ( 12+ 1 - 14)= 0
?? = -8
p ? = c - 8b
?
p ? = -31i ˆ - 11j ˆ - 52k
ˆ
So, p ? · ( i ˆ - j ˆ - k
ˆ
)
= -31+ 11+ 52
= 32
Q3: The distance of the point ?? ( ?? ,?? ,-?? ) form the line passing through the point ?? ( ?? ,-?? ,?? ) and
perpendicular to the lines ??? = ( -?? ??ˆ + ?? ?? ˆ
)+ ?? ( ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
) ,?? ? R and ??? = ( ??ˆ - ?? ??ˆ + ?? ˆ
)+ ?? ( -??ˆ +
?? ??ˆ + ?? ?? ˆ
) ,?? ? R is :
(A) v????
(B) v????
(C) v????
(D) v???? [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (a)
A vector in the direction of the required line can be obtained by cross product of
|
??ˆ ??ˆ ?? ˆ
2 3 5
-1 3 2
|
= -9??ˆ - 9??ˆ + 9?? ˆ
Required line
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? '
( -9i ˆ - 9j ˆ + 9k
ˆ
)
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? ( i ˆ + j ˆ - k
ˆ
)
Now distance of ( 0,2,-2)
P.V. of P = ( 5 + ?? ) ??ˆ + ( ?? - 4) ??ˆ + ( 3 - ?? ) ?? ˆ
AP
?????
= ( 5 + ?? ) ??ˆ + ( ?? - 6) ??ˆ + ( 5 - ?? ) ?? ˆ
AP
?????
· ( i ˆ + j ˆ - k
ˆ
)= 0
5 + ?? + ?? - 6 - 5 + ?? = 0
?? = 2
|AP
?????
| = v49 + 16 + 9
|AP
?????
| = v74
Q4: Let ?? ?? :??? = ( ??ˆ - ??ˆ + ?? ?? ˆ
)+ ?? ( ??ˆ - ??ˆ + ?? ?? ˆ
) ,?? ? R,
?? ?? :??? = ( ??ˆ - ?? ˆ
)+ ?? ( ?? ??ˆ + ??ˆ + ?? ?? ˆ
) ,?? ? R, and ?? ?? :??? = ?? ( ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
) ,?? ? R
be three lines such that ?? ?? is perpendicular to ?? ?? and ?? ?? is perpendicular to both ?? ?? and ?? ?? . Then, the
point which lies on ?? ?? is
(A) ( ?? ,?? ,-?? )
(B) ( ?? ,-?? ,?? )
(C) ( -?? ,?? ,?? )
(D) ( -,?? - ?? ,?? ) [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (c)
L
1
? L
2
L
3
? L
1
, L
2
3 - 1 + 2P = 0
P = -1
|
i ˆ j ˆ k
ˆ
1 -1 2
3 1 -1
| = -i ˆ + 7j ˆ + 4k
ˆ
? ( -?? ,7?? ,4?? ) will lie on L
3
For ?? = 1 the point will be ( -1,7,4)
Q5: Let ??? ? = ??ˆ + ?? ??ˆ + ?? ?? ˆ
,?? ,?? ? R. Let a vector ?? ? ?
be such that the angle between ??? ? and ?? ? ?
is
?? ?? and
|?? ? ?
|
?? = ?? . If ??? ? · ?? ? ?
= ?? v?? , then the value of ( ?? ?? + ?? ?? ) |??? ? × ?? ? ?
|
?? is equal to
A. 85
B. 90
C. 75
D. 95 [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (b)
|b
?
|
2
= 6;|a ? ||b
?
|cos ?? = 3v2
|a ? |
2
|b
?
|
2
cos
2
?? = 18
|a ? |
2
= 6
Also 1 + ?? 2
+ ?? 2
= 6
?? 2
+ ?? 2
= 5
to find
( ?? 2
+ ?? 2
) |?? |
2
|?? ?
|
2
sin
2
?? = ( 5) ( 6) ( 6)(
1
2
)
= 90
Q6: Let ?? and ?? ?
be two vectors such that |?? ?
| = 1 and |?? ?
× ?? | = 2. Then |( ?? ?
× ?? )- ?? ?
|
2
is equal to
(A) 1
(B) 3
(C) 5
(D) 4 [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (c)
|?? ?
| = 1&|?? ?
× ?? | = 2
( ?? ?
× ?? )· ?? ?
= ?? ?
· ( ?? ?
× ?? )= 0
|( ?? ?
× ?? )- ?? ?
|
2
= |?? ?
× ?? |
2
+ |?? ?
|
2
= 4 + 1 = 5
Q7: Let ??? = ?? ?? ??ˆ + ?? ?? ??ˆ + ?? ?? ?? ˆ
and ??
= ?? ?? ??ˆ
ˆ
+ ?? ?? ??ˆ + ?? ?? ?? ˆ
be two vectors such that |??? | = ?? ,??? ? · ?? ? ?
= ??
and |?? ? ?
| = ?? . If ??? = ?? ( ??? ? × ?? ? ?
)- ?? ?? ? ?
, then the angle between ?? ? ?
and ??? is equal to:
(A) ?????? -?? (-
?? v?? )
(B) ?????? -?? (
?? ?? )
(C) ?????? -?? (
?? v?? )
(D) ?????? -?? ( -
v?? ?? ) [JEE Main 2024 (Online) 30th January Morning Shift]
Ans: (d)
Given |?? | = 1,|?? ?
| = 4,?? · ?? ?
= 2
?? = 2( ?? × ?? ?
)- 3?? ?
Dot product with a ? on both sides
?? . ?? ?? = -6…
Dot product with ?? ?
on both sides
bc
????
= -48 …( 2)
c · c = 4a ? × b
?
|
2
+ 9|b
?
|
2
|c |
2
= 4[|a|
2
| b|
2
- ( a · b
?
)
2
] + 9|b
?
|
2
|c |
2
= 4[( 1) ( 4)
2
- ( 4) ] + 9( 16)
|c |
2
= 4[12] + 144
|c |
2
= 48 + 144
|c |
2
= 192
Page 5
JEE Mains Previous Year Questions
(2021-2024): Vector Algebra
2024
Q1: Let ??? = -?? ??ˆ + ??ˆ - ?? ?? ˆ
,??
= ??ˆ + ?? ??ˆ - ?? ?? ˆ
and
?? = ( ( ??? × ??
)× ??ˆ)× ??ˆ)× ??ˆ. Then ??? · ( -??ˆ + ??ˆ + ?? ˆ
) is equal to :
(A) -12
(B) -10
(C) -13
(D) -15 [JEE Main 2024 (Online) 1st February Morning Shift]
Ans: (a)
?? = -5 · ??ˆ + ??ˆ - 3?? ˆ
,?? ?
= ??ˆ + 2??ˆ - 4?? ˆ
?? = ( ( ( ?? × ?? ?
)× ??ˆ)× ??ˆ)× ??ˆ
= ( ( ( ?? · ??ˆ) ?? ?
- ( ?? ?
· ??ˆ) ?? )× ??ˆ)× ??ˆ
= ( ( -5?? ?
- ?? )× ??ˆ)× ??ˆ
= ( ( -11??ˆ + 23?? ˆ
)× ??ˆ)× ??ˆ
= ( 11?? ˆ
+ 23??ˆ)× ??ˆ
= ( 11??ˆ - 23?? ˆ
)
?? · ( -??ˆ + ??ˆ + ?? ˆ
)= 0 + 11- 23
= -12
Q2: Let ??? ? = ?? ??ˆ + ??ˆ - ?? ?? ˆ
,?? ? ?
= ?? ??ˆ + ??ˆ + ?? ?? ˆ
and ??? = ??ˆ - ?? ??ˆ + ?? ?? ˆ
be three vectors. If a vectors ??? ?
satisfies ??? ? × ?? ? ?
= ??? × ?? ? ?
and ??? ? · ??? ? = ?? , then ??? ? · ( ??ˆ - ??ˆ - ?? ˆ
) is equal to
(A)24
(B) 32
(C) 36
(D )28 [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (b)
?? × ?? ?
- ?? × ?? ?
= 0
?
( ?? - ?? )× ?? ?
= 0
?
?? - ?? = ?? ?? ?
? ?? = ?? + ?? ?? ?
Now, p ? · a ? = 0 (given)
So, c · a ? + ?? a ? · b
?
= 0
( 3 - 3 - 8)+ ?? ( 12+ 1 - 14)= 0
?? = -8
p ? = c - 8b
?
p ? = -31i ˆ - 11j ˆ - 52k
ˆ
So, p ? · ( i ˆ - j ˆ - k
ˆ
)
= -31+ 11+ 52
= 32
Q3: The distance of the point ?? ( ?? ,?? ,-?? ) form the line passing through the point ?? ( ?? ,-?? ,?? ) and
perpendicular to the lines ??? = ( -?? ??ˆ + ?? ?? ˆ
)+ ?? ( ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
) ,?? ? R and ??? = ( ??ˆ - ?? ??ˆ + ?? ˆ
)+ ?? ( -??ˆ +
?? ??ˆ + ?? ?? ˆ
) ,?? ? R is :
(A) v????
(B) v????
(C) v????
(D) v???? [JEE Main 2024 (Online) 31st January Morning Shift]
Ans: (a)
A vector in the direction of the required line can be obtained by cross product of
|
??ˆ ??ˆ ?? ˆ
2 3 5
-1 3 2
|
= -9??ˆ - 9??ˆ + 9?? ˆ
Required line
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? '
( -9i ˆ - 9j ˆ + 9k
ˆ
)
r = ( 5i ˆ - 4j ˆ + 3k
ˆ
)+ ?? ( i ˆ + j ˆ - k
ˆ
)
Now distance of ( 0,2,-2)
P.V. of P = ( 5 + ?? ) ??ˆ + ( ?? - 4) ??ˆ + ( 3 - ?? ) ?? ˆ
AP
?????
= ( 5 + ?? ) ??ˆ + ( ?? - 6) ??ˆ + ( 5 - ?? ) ?? ˆ
AP
?????
· ( i ˆ + j ˆ - k
ˆ
)= 0
5 + ?? + ?? - 6 - 5 + ?? = 0
?? = 2
|AP
?????
| = v49 + 16 + 9
|AP
?????
| = v74
Q4: Let ?? ?? :??? = ( ??ˆ - ??ˆ + ?? ?? ˆ
)+ ?? ( ??ˆ - ??ˆ + ?? ?? ˆ
) ,?? ? R,
?? ?? :??? = ( ??ˆ - ?? ˆ
)+ ?? ( ?? ??ˆ + ??ˆ + ?? ?? ˆ
) ,?? ? R, and ?? ?? :??? = ?? ( ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
) ,?? ? R
be three lines such that ?? ?? is perpendicular to ?? ?? and ?? ?? is perpendicular to both ?? ?? and ?? ?? . Then, the
point which lies on ?? ?? is
(A) ( ?? ,?? ,-?? )
(B) ( ?? ,-?? ,?? )
(C) ( -?? ,?? ,?? )
(D) ( -,?? - ?? ,?? ) [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (c)
L
1
? L
2
L
3
? L
1
, L
2
3 - 1 + 2P = 0
P = -1
|
i ˆ j ˆ k
ˆ
1 -1 2
3 1 -1
| = -i ˆ + 7j ˆ + 4k
ˆ
? ( -?? ,7?? ,4?? ) will lie on L
3
For ?? = 1 the point will be ( -1,7,4)
Q5: Let ??? ? = ??ˆ + ?? ??ˆ + ?? ?? ˆ
,?? ,?? ? R. Let a vector ?? ? ?
be such that the angle between ??? ? and ?? ? ?
is
?? ?? and
|?? ? ?
|
?? = ?? . If ??? ? · ?? ? ?
= ?? v?? , then the value of ( ?? ?? + ?? ?? ) |??? ? × ?? ? ?
|
?? is equal to
A. 85
B. 90
C. 75
D. 95 [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (b)
|b
?
|
2
= 6;|a ? ||b
?
|cos ?? = 3v2
|a ? |
2
|b
?
|
2
cos
2
?? = 18
|a ? |
2
= 6
Also 1 + ?? 2
+ ?? 2
= 6
?? 2
+ ?? 2
= 5
to find
( ?? 2
+ ?? 2
) |?? |
2
|?? ?
|
2
sin
2
?? = ( 5) ( 6) ( 6)(
1
2
)
= 90
Q6: Let ?? and ?? ?
be two vectors such that |?? ?
| = 1 and |?? ?
× ?? | = 2. Then |( ?? ?
× ?? )- ?? ?
|
2
is equal to
(A) 1
(B) 3
(C) 5
(D) 4 [JEE Main 2024 (Online) 30th January Evening Shift]
Ans: (c)
|?? ?
| = 1&|?? ?
× ?? | = 2
( ?? ?
× ?? )· ?? ?
= ?? ?
· ( ?? ?
× ?? )= 0
|( ?? ?
× ?? )- ?? ?
|
2
= |?? ?
× ?? |
2
+ |?? ?
|
2
= 4 + 1 = 5
Q7: Let ??? = ?? ?? ??ˆ + ?? ?? ??ˆ + ?? ?? ?? ˆ
and ??
= ?? ?? ??ˆ
ˆ
+ ?? ?? ??ˆ + ?? ?? ?? ˆ
be two vectors such that |??? | = ?? ,??? ? · ?? ? ?
= ??
and |?? ? ?
| = ?? . If ??? = ?? ( ??? ? × ?? ? ?
)- ?? ?? ? ?
, then the angle between ?? ? ?
and ??? is equal to:
(A) ?????? -?? (-
?? v?? )
(B) ?????? -?? (
?? ?? )
(C) ?????? -?? (
?? v?? )
(D) ?????? -?? ( -
v?? ?? ) [JEE Main 2024 (Online) 30th January Morning Shift]
Ans: (d)
Given |?? | = 1,|?? ?
| = 4,?? · ?? ?
= 2
?? = 2( ?? × ?? ?
)- 3?? ?
Dot product with a ? on both sides
?? . ?? ?? = -6…
Dot product with ?? ?
on both sides
bc
????
= -48 …( 2)
c · c = 4a ? × b
?
|
2
+ 9|b
?
|
2
|c |
2
= 4[|a|
2
| b|
2
- ( a · b
?
)
2
] + 9|b
?
|
2
|c |
2
= 4[( 1) ( 4)
2
- ( 4) ] + 9( 16)
|c |
2
= 4[12] + 144
|c |
2
= 48 + 144
|c |
2
= 192
? cos ?? =
b
?
· c
|b
?
c |
???????
? cos ?? =
-48
v192· 4
? cos ?? =
-48
8v3 · 4
? cos ?? =
-3
2v3
? cos ?? =
-v3
2
? ?? = cos
-1
(
-v3
2
)
Q8: Let a unit vector ?? ˆ = ?? ??ˆ + ?? ??ˆ + ?? ?? ˆ
make angles
?? ?? ,
?? ?? and
?? ?? ?? with the vectors
?? v?? ??ˆ +
?? v?? ?? ˆ
,
?? v?? ??ˆ +
?? v?? ?? ˆ
and
?? v?? ??ˆ +
?? v?? ??ˆ respectively. If ??? ? =
?? v?? ??ˆ +
?? v?? ??ˆ +
?? v?? ?? ˆ
then |??ˆ - ??? ? |
?? is equal to
A.
????
??
B.
?? ??
C. 7
D. 9 [JEE Main 2024 (Online) 29th January Evening Shift]
Ans: (b)
Unit vector u ˆ = xi ˆ + yj ˆ + zk
p
1
???? =
1
v2
i ˆ +
1
v2
k
ˆ
,p ? 2 =
1
v2
j ˆ +
1
v2
k
ˆ
p ? 3 =
1
v2
i ˆ +
1
v2
j ˆ
Now angle between u ˆ and p ?
1
=
?? 2
u ˆ · p ?
1
= 0 ?
x
v2
+
z
v2
= 0
? x + z = 0…… (i)
Angle between u ˆ and p ?
2
=
?? 3
u ˆ · p
2
???? = |u ˆ|· |p
2
???? |cos
?? 3
?
?? v2
+
?? v2
=
1
2
? ?? + ?? =
1
v2
Angle between u ˆ and p ?
3
=
2?? 3
u ˆ · p ?
3
= |u ˆ|· |P
? ?
3|cos
2?? 3
?
?? v2
+
4
v2
=
-1
2
? ?? + ?? =
-1
v2
…..
Read More