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 Page 1


JEE Solved Example on Parabola 
JEE Mains 
Q1: The length of the chord intercepted by the parabola ?? ?? = ?? ?? on the straight line ?? + ?? = ?? is- 
(A) 4 
(B) ?? v ?? 
(C) 8 
(D) ?? v ?? 
 Ans: (C) ?? = 1 - ?? ? ?? 2
= 4 - 4?? ? ?? 2
+ 4?? - 4 = 0
( ?? 2
- ?? 1
)
2
= ( 4)
2
+ 4 × 4 = 32 ? |?? 2
- ?? 1
| = 4v 2
|?? 2
- ?? 1
| = ( 1 - ?? 2
)- ( 1 - ?? 1
) = |?? 2
- ?? 1
|
 ? Length of chord = v 2 × |?? 2
- ?? 1
| = 8
 
 
 
Q2:  A parabola is drawn with its focus at ( ?? , ?? ) and vertex at the focus of the parabola ?? ?? -
???? ?? - ?? ?? + ?? = 0 . The equation of the parabola is - 
(A) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(B) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(C) ?? ?? - ?? ?? + ?? ?? - ???? = ?? 
(D) ?? ?? + ?? ?? - ?? ?? - ???? = ?? 
Ans: (A) ?? 2
- 12?? - 4?? + 4 = 0 
( ?? - 2)
2
= 12?? 
Let ?? = ?? and ?? = ?? + 2 
? ?? 2
= 12?? 
Focus of parabola is ( 3,0) 
? Focus in original coordinate system is ( 3,2) 
? Vertex of new parabola is ( 3,2) &focus = ( 3,4) 
? ?? = 2 
Let ?? = ?? + 3&?? = ?? + 2 
? Equation is ?? 2
= 8?? ? ( ?? - 3)
2
= 8( ?? - 2) 
? ?? 2
- 6?? - 8?? + 25 = 0 is the equation of parabola 
 
Page 2


JEE Solved Example on Parabola 
JEE Mains 
Q1: The length of the chord intercepted by the parabola ?? ?? = ?? ?? on the straight line ?? + ?? = ?? is- 
(A) 4 
(B) ?? v ?? 
(C) 8 
(D) ?? v ?? 
 Ans: (C) ?? = 1 - ?? ? ?? 2
= 4 - 4?? ? ?? 2
+ 4?? - 4 = 0
( ?? 2
- ?? 1
)
2
= ( 4)
2
+ 4 × 4 = 32 ? |?? 2
- ?? 1
| = 4v 2
|?? 2
- ?? 1
| = ( 1 - ?? 2
)- ( 1 - ?? 1
) = |?? 2
- ?? 1
|
 ? Length of chord = v 2 × |?? 2
- ?? 1
| = 8
 
 
 
Q2:  A parabola is drawn with its focus at ( ?? , ?? ) and vertex at the focus of the parabola ?? ?? -
???? ?? - ?? ?? + ?? = 0 . The equation of the parabola is - 
(A) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(B) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(C) ?? ?? - ?? ?? + ?? ?? - ???? = ?? 
(D) ?? ?? + ?? ?? - ?? ?? - ???? = ?? 
Ans: (A) ?? 2
- 12?? - 4?? + 4 = 0 
( ?? - 2)
2
= 12?? 
Let ?? = ?? and ?? = ?? + 2 
? ?? 2
= 12?? 
Focus of parabola is ( 3,0) 
? Focus in original coordinate system is ( 3,2) 
? Vertex of new parabola is ( 3,2) &focus = ( 3,4) 
? ?? = 2 
Let ?? = ?? + 3&?? = ?? + 2 
? Equation is ?? 2
= 8?? ? ( ?? - 3)
2
= 8( ?? - 2) 
? ?? 2
- 6?? - 8?? + 25 = 0 is the equation of parabola 
 
Q3:  The curve describes parametrically by ?? = ?? ?? - ?? ?? + ?? , ?? = ?? ?? + ???? + ?? represents- 
(A) Straight line 
(B) Pair of straight line 
(C) Circle 
(D) Parabola 
Ans: (D) ?? = ?? 2
- 2?? + 2, ?? = ?? 2
+ 2?? + 2 
?? + ?? - 4 = 2?? 2
?? - ?? = 4?? 
? ( ?? + ?? - 4, ?? - ?? ) lies on a parabola 
? ( ?? + ?? , ?? - ?? ) lies on a parabola by rotating axis ( ?? , ?? ) lies on parabola 
 
 
Q4:  If ?? = ?? ?? - ?? is a tangent to the parabola ?? ?? = ?? ?? (?? -
?? ?? ), then 'a' is equal to- 
(A) 1 
(B) -1 
(C) 
????
?? 
(D) 
-????
?? 
Ans: (D) ?? 2
= 4?? (?? -
1
3
) 
Let ?? = ?? and ?? = ?? +
1
3
 
? Equation of parabola is ?? 2
= 4???? 
? equation of line is ?? = 2?? -
7
3
 
?? =
?? ?? ? -
7
3
=
?? 2
 ? ?? = -
14
3
 
 
 
Q5:  Two tangents to the parabola ?? ?? = ?? a make angles ?? ?? and ?? ?? with the ?? -axis. The locus of 
their point of intersection if 
?????? ?? ?? ?????? ?? ?? = ?? is- 
(A) ?? ?? ?? = ?????? 
(B) ?? ?? ?? = ?????? 
(C) ?? ?? = ?? ???? 
(D) None 
Page 3


JEE Solved Example on Parabola 
JEE Mains 
Q1: The length of the chord intercepted by the parabola ?? ?? = ?? ?? on the straight line ?? + ?? = ?? is- 
(A) 4 
(B) ?? v ?? 
(C) 8 
(D) ?? v ?? 
 Ans: (C) ?? = 1 - ?? ? ?? 2
= 4 - 4?? ? ?? 2
+ 4?? - 4 = 0
( ?? 2
- ?? 1
)
2
= ( 4)
2
+ 4 × 4 = 32 ? |?? 2
- ?? 1
| = 4v 2
|?? 2
- ?? 1
| = ( 1 - ?? 2
)- ( 1 - ?? 1
) = |?? 2
- ?? 1
|
 ? Length of chord = v 2 × |?? 2
- ?? 1
| = 8
 
 
 
Q2:  A parabola is drawn with its focus at ( ?? , ?? ) and vertex at the focus of the parabola ?? ?? -
???? ?? - ?? ?? + ?? = 0 . The equation of the parabola is - 
(A) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(B) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(C) ?? ?? - ?? ?? + ?? ?? - ???? = ?? 
(D) ?? ?? + ?? ?? - ?? ?? - ???? = ?? 
Ans: (A) ?? 2
- 12?? - 4?? + 4 = 0 
( ?? - 2)
2
= 12?? 
Let ?? = ?? and ?? = ?? + 2 
? ?? 2
= 12?? 
Focus of parabola is ( 3,0) 
? Focus in original coordinate system is ( 3,2) 
? Vertex of new parabola is ( 3,2) &focus = ( 3,4) 
? ?? = 2 
Let ?? = ?? + 3&?? = ?? + 2 
? Equation is ?? 2
= 8?? ? ( ?? - 3)
2
= 8( ?? - 2) 
? ?? 2
- 6?? - 8?? + 25 = 0 is the equation of parabola 
 
Q3:  The curve describes parametrically by ?? = ?? ?? - ?? ?? + ?? , ?? = ?? ?? + ???? + ?? represents- 
(A) Straight line 
(B) Pair of straight line 
(C) Circle 
(D) Parabola 
Ans: (D) ?? = ?? 2
- 2?? + 2, ?? = ?? 2
+ 2?? + 2 
?? + ?? - 4 = 2?? 2
?? - ?? = 4?? 
? ( ?? + ?? - 4, ?? - ?? ) lies on a parabola 
? ( ?? + ?? , ?? - ?? ) lies on a parabola by rotating axis ( ?? , ?? ) lies on parabola 
 
 
Q4:  If ?? = ?? ?? - ?? is a tangent to the parabola ?? ?? = ?? ?? (?? -
?? ?? ), then 'a' is equal to- 
(A) 1 
(B) -1 
(C) 
????
?? 
(D) 
-????
?? 
Ans: (D) ?? 2
= 4?? (?? -
1
3
) 
Let ?? = ?? and ?? = ?? +
1
3
 
? Equation of parabola is ?? 2
= 4???? 
? equation of line is ?? = 2?? -
7
3
 
?? =
?? ?? ? -
7
3
=
?? 2
 ? ?? = -
14
3
 
 
 
Q5:  Two tangents to the parabola ?? ?? = ?? a make angles ?? ?? and ?? ?? with the ?? -axis. The locus of 
their point of intersection if 
?????? ?? ?? ?????? ?? ?? = ?? is- 
(A) ?? ?? ?? = ?????? 
(B) ?? ?? ?? = ?????? 
(C) ?? ?? = ?? ???? 
(D) None 
Ans: ( ?? ) cota
1
= 2cota
2
? tana
1
=
tan ?? 2
2
 let ?? = ( ?? ?? 1
2
, 2?? ?? 1
) &?? = ( ?? ?? 2
2
, 2?? ?? 2
)
?? = point of intersection = ( ?? ?? 1
?? 2
, ?? ( ?? 1
+ ?? 2
) ) = ( ?? , ?? )
 Slope of ?? =
1
?? 1
 and slope of ?? =
1
?? 2
 ?
1
?? 1
=
1
2?? 2
 ? ?? 1
= 2?? 2
 ? ?? = 2?? ?? 2
2
 ?? = 3?? ?? 2
 ? (
?? 3?? )
2
× 2?? = ?? ? 2?? 2
= 9???? is locus of ?? 
 
Q6:  Through the vertex ' ?? ' of the parabola ?? ?? = ?? ???? , variable chords ???? and ???? are drawn at 
right angles. If the variable chord ???? intersects the axis of ?? at ?? , then distance OR- 
(A) Varies with different positions of ?? and ?? 
(B) Equals the semi latus rectum of the parabola 
(C) Equals latus rectum of the parabola 
(D) Equals double the latus rectum of the parabola 
Ans: (C) Let P be ( ?? ?? 1
2
, 2?? ?? 1
) and ?? be ( ?? ?? 2
2
, 2?? ?? 2
) 
OP ? OQ
 ?
2t
1
t
1
2
×
2t
2
t
2
2
= -1
 ? t
2
= -
4
t
1
 
The equation of PQ is 
( ?? - ?? ?? 1
) =
2
?? 1
-
4
?? 1
( ?? - ?? ?? 1
2
)
?? ?? = (?? 1
-
4
?? 1
) ×
-2????
2
+ ?? ?? 1
2
= 4?? ? ?? = ( 0,4?? ) ? ???? = 4?? 
 
 
 
 
 
Page 4


JEE Solved Example on Parabola 
JEE Mains 
Q1: The length of the chord intercepted by the parabola ?? ?? = ?? ?? on the straight line ?? + ?? = ?? is- 
(A) 4 
(B) ?? v ?? 
(C) 8 
(D) ?? v ?? 
 Ans: (C) ?? = 1 - ?? ? ?? 2
= 4 - 4?? ? ?? 2
+ 4?? - 4 = 0
( ?? 2
- ?? 1
)
2
= ( 4)
2
+ 4 × 4 = 32 ? |?? 2
- ?? 1
| = 4v 2
|?? 2
- ?? 1
| = ( 1 - ?? 2
)- ( 1 - ?? 1
) = |?? 2
- ?? 1
|
 ? Length of chord = v 2 × |?? 2
- ?? 1
| = 8
 
 
 
Q2:  A parabola is drawn with its focus at ( ?? , ?? ) and vertex at the focus of the parabola ?? ?? -
???? ?? - ?? ?? + ?? = 0 . The equation of the parabola is - 
(A) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(B) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(C) ?? ?? - ?? ?? + ?? ?? - ???? = ?? 
(D) ?? ?? + ?? ?? - ?? ?? - ???? = ?? 
Ans: (A) ?? 2
- 12?? - 4?? + 4 = 0 
( ?? - 2)
2
= 12?? 
Let ?? = ?? and ?? = ?? + 2 
? ?? 2
= 12?? 
Focus of parabola is ( 3,0) 
? Focus in original coordinate system is ( 3,2) 
? Vertex of new parabola is ( 3,2) &focus = ( 3,4) 
? ?? = 2 
Let ?? = ?? + 3&?? = ?? + 2 
? Equation is ?? 2
= 8?? ? ( ?? - 3)
2
= 8( ?? - 2) 
? ?? 2
- 6?? - 8?? + 25 = 0 is the equation of parabola 
 
Q3:  The curve describes parametrically by ?? = ?? ?? - ?? ?? + ?? , ?? = ?? ?? + ???? + ?? represents- 
(A) Straight line 
(B) Pair of straight line 
(C) Circle 
(D) Parabola 
Ans: (D) ?? = ?? 2
- 2?? + 2, ?? = ?? 2
+ 2?? + 2 
?? + ?? - 4 = 2?? 2
?? - ?? = 4?? 
? ( ?? + ?? - 4, ?? - ?? ) lies on a parabola 
? ( ?? + ?? , ?? - ?? ) lies on a parabola by rotating axis ( ?? , ?? ) lies on parabola 
 
 
Q4:  If ?? = ?? ?? - ?? is a tangent to the parabola ?? ?? = ?? ?? (?? -
?? ?? ), then 'a' is equal to- 
(A) 1 
(B) -1 
(C) 
????
?? 
(D) 
-????
?? 
Ans: (D) ?? 2
= 4?? (?? -
1
3
) 
Let ?? = ?? and ?? = ?? +
1
3
 
? Equation of parabola is ?? 2
= 4???? 
? equation of line is ?? = 2?? -
7
3
 
?? =
?? ?? ? -
7
3
=
?? 2
 ? ?? = -
14
3
 
 
 
Q5:  Two tangents to the parabola ?? ?? = ?? a make angles ?? ?? and ?? ?? with the ?? -axis. The locus of 
their point of intersection if 
?????? ?? ?? ?????? ?? ?? = ?? is- 
(A) ?? ?? ?? = ?????? 
(B) ?? ?? ?? = ?????? 
(C) ?? ?? = ?? ???? 
(D) None 
Ans: ( ?? ) cota
1
= 2cota
2
? tana
1
=
tan ?? 2
2
 let ?? = ( ?? ?? 1
2
, 2?? ?? 1
) &?? = ( ?? ?? 2
2
, 2?? ?? 2
)
?? = point of intersection = ( ?? ?? 1
?? 2
, ?? ( ?? 1
+ ?? 2
) ) = ( ?? , ?? )
 Slope of ?? =
1
?? 1
 and slope of ?? =
1
?? 2
 ?
1
?? 1
=
1
2?? 2
 ? ?? 1
= 2?? 2
 ? ?? = 2?? ?? 2
2
 ?? = 3?? ?? 2
 ? (
?? 3?? )
2
× 2?? = ?? ? 2?? 2
= 9???? is locus of ?? 
 
Q6:  Through the vertex ' ?? ' of the parabola ?? ?? = ?? ???? , variable chords ???? and ???? are drawn at 
right angles. If the variable chord ???? intersects the axis of ?? at ?? , then distance OR- 
(A) Varies with different positions of ?? and ?? 
(B) Equals the semi latus rectum of the parabola 
(C) Equals latus rectum of the parabola 
(D) Equals double the latus rectum of the parabola 
Ans: (C) Let P be ( ?? ?? 1
2
, 2?? ?? 1
) and ?? be ( ?? ?? 2
2
, 2?? ?? 2
) 
OP ? OQ
 ?
2t
1
t
1
2
×
2t
2
t
2
2
= -1
 ? t
2
= -
4
t
1
 
The equation of PQ is 
( ?? - ?? ?? 1
) =
2
?? 1
-
4
?? 1
( ?? - ?? ?? 1
2
)
?? ?? = (?? 1
-
4
?? 1
) ×
-2????
2
+ ?? ?? 1
2
= 4?? ? ?? = ( 0,4?? ) ? ???? = 4?? 
 
 
 
 
 
 
Q7:  A point ?? moves such that the difference between its distances from the origin and from the 
axis of ' ?? ' is always a constant ?? . The locus- 
(A) A straight line having equal intercepts ?? on the axis 
(B) A circle having its centre at (?? , -
?? ?? ) & passing through (?? v ?? ,
?? ?? ) 
(C) A parabola with its vertex at (?? , -
?? ?? ) & passing through (?? v ?? ,
?? ?? ) 
(D) None of these 
Ans: (C) v?? 2
+ ?? 2
- ?? = ?? 
? ?? 2
+ ?? 2
= ?? 2
+ 2???? + ?? 2
 
?? 2
= 2?? (?? +
?? 2
) ? Vertex is (0, -
?? 2
) 
It passes through (?? v 2,
?? 2
) 
 
 
Q8: Tangents are drawn from the point ( -?? , ?? ) on the parabola ?? ?? = ?? ?? . The length, these 
tangents will intercept on the line ?? = ?? , is- 
(A) 6 
(B) ?? v ?? 
(C) ?? v ?? 
(D) None 
Ans: (B) Equation of tangent is ?? = ???? +
1
?? ( -1,2) lies on it, then 
2 = -?? +
1
?? ? ?? 2
+ 2?? - 1 = 0
?? = 2, so ?? 1
- ?? 2
= 2( ?? 1
- ?? 2
)+
?? 2
- ?? 1
?? 1
?? 2
 ? ( ?? - ?? 2
)
2
= ( ?? 1
- ?? 2
)
2
(2 -
1
?? 1
?? 2
)
2
 = [( ?? 1
+ ?? 2
)
2
- 4?? 1
?? 2
] (2 -
1
?? 1
?? 2
)
2
 = [( ?? 1
+ ?? 2
)
2
- 4?? 1
?? 2
] (2 -
1
?? 1
?? 2
)
2
( ?? 1
- ?? 2
)
2
= ( 4 + 4) ( 2 + 1)
2
= 8 × 9
 ? |?? 1
- ?? 2
| = 6v 2
 
 
 
 
Page 5


JEE Solved Example on Parabola 
JEE Mains 
Q1: The length of the chord intercepted by the parabola ?? ?? = ?? ?? on the straight line ?? + ?? = ?? is- 
(A) 4 
(B) ?? v ?? 
(C) 8 
(D) ?? v ?? 
 Ans: (C) ?? = 1 - ?? ? ?? 2
= 4 - 4?? ? ?? 2
+ 4?? - 4 = 0
( ?? 2
- ?? 1
)
2
= ( 4)
2
+ 4 × 4 = 32 ? |?? 2
- ?? 1
| = 4v 2
|?? 2
- ?? 1
| = ( 1 - ?? 2
)- ( 1 - ?? 1
) = |?? 2
- ?? 1
|
 ? Length of chord = v 2 × |?? 2
- ?? 1
| = 8
 
 
 
Q2:  A parabola is drawn with its focus at ( ?? , ?? ) and vertex at the focus of the parabola ?? ?? -
???? ?? - ?? ?? + ?? = 0 . The equation of the parabola is - 
(A) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(B) ?? ?? - ?? ?? - ?? ?? + ???? = ?? 
(C) ?? ?? - ?? ?? + ?? ?? - ???? = ?? 
(D) ?? ?? + ?? ?? - ?? ?? - ???? = ?? 
Ans: (A) ?? 2
- 12?? - 4?? + 4 = 0 
( ?? - 2)
2
= 12?? 
Let ?? = ?? and ?? = ?? + 2 
? ?? 2
= 12?? 
Focus of parabola is ( 3,0) 
? Focus in original coordinate system is ( 3,2) 
? Vertex of new parabola is ( 3,2) &focus = ( 3,4) 
? ?? = 2 
Let ?? = ?? + 3&?? = ?? + 2 
? Equation is ?? 2
= 8?? ? ( ?? - 3)
2
= 8( ?? - 2) 
? ?? 2
- 6?? - 8?? + 25 = 0 is the equation of parabola 
 
Q3:  The curve describes parametrically by ?? = ?? ?? - ?? ?? + ?? , ?? = ?? ?? + ???? + ?? represents- 
(A) Straight line 
(B) Pair of straight line 
(C) Circle 
(D) Parabola 
Ans: (D) ?? = ?? 2
- 2?? + 2, ?? = ?? 2
+ 2?? + 2 
?? + ?? - 4 = 2?? 2
?? - ?? = 4?? 
? ( ?? + ?? - 4, ?? - ?? ) lies on a parabola 
? ( ?? + ?? , ?? - ?? ) lies on a parabola by rotating axis ( ?? , ?? ) lies on parabola 
 
 
Q4:  If ?? = ?? ?? - ?? is a tangent to the parabola ?? ?? = ?? ?? (?? -
?? ?? ), then 'a' is equal to- 
(A) 1 
(B) -1 
(C) 
????
?? 
(D) 
-????
?? 
Ans: (D) ?? 2
= 4?? (?? -
1
3
) 
Let ?? = ?? and ?? = ?? +
1
3
 
? Equation of parabola is ?? 2
= 4???? 
? equation of line is ?? = 2?? -
7
3
 
?? =
?? ?? ? -
7
3
=
?? 2
 ? ?? = -
14
3
 
 
 
Q5:  Two tangents to the parabola ?? ?? = ?? a make angles ?? ?? and ?? ?? with the ?? -axis. The locus of 
their point of intersection if 
?????? ?? ?? ?????? ?? ?? = ?? is- 
(A) ?? ?? ?? = ?????? 
(B) ?? ?? ?? = ?????? 
(C) ?? ?? = ?? ???? 
(D) None 
Ans: ( ?? ) cota
1
= 2cota
2
? tana
1
=
tan ?? 2
2
 let ?? = ( ?? ?? 1
2
, 2?? ?? 1
) &?? = ( ?? ?? 2
2
, 2?? ?? 2
)
?? = point of intersection = ( ?? ?? 1
?? 2
, ?? ( ?? 1
+ ?? 2
) ) = ( ?? , ?? )
 Slope of ?? =
1
?? 1
 and slope of ?? =
1
?? 2
 ?
1
?? 1
=
1
2?? 2
 ? ?? 1
= 2?? 2
 ? ?? = 2?? ?? 2
2
 ?? = 3?? ?? 2
 ? (
?? 3?? )
2
× 2?? = ?? ? 2?? 2
= 9???? is locus of ?? 
 
Q6:  Through the vertex ' ?? ' of the parabola ?? ?? = ?? ???? , variable chords ???? and ???? are drawn at 
right angles. If the variable chord ???? intersects the axis of ?? at ?? , then distance OR- 
(A) Varies with different positions of ?? and ?? 
(B) Equals the semi latus rectum of the parabola 
(C) Equals latus rectum of the parabola 
(D) Equals double the latus rectum of the parabola 
Ans: (C) Let P be ( ?? ?? 1
2
, 2?? ?? 1
) and ?? be ( ?? ?? 2
2
, 2?? ?? 2
) 
OP ? OQ
 ?
2t
1
t
1
2
×
2t
2
t
2
2
= -1
 ? t
2
= -
4
t
1
 
The equation of PQ is 
( ?? - ?? ?? 1
) =
2
?? 1
-
4
?? 1
( ?? - ?? ?? 1
2
)
?? ?? = (?? 1
-
4
?? 1
) ×
-2????
2
+ ?? ?? 1
2
= 4?? ? ?? = ( 0,4?? ) ? ???? = 4?? 
 
 
 
 
 
 
Q7:  A point ?? moves such that the difference between its distances from the origin and from the 
axis of ' ?? ' is always a constant ?? . The locus- 
(A) A straight line having equal intercepts ?? on the axis 
(B) A circle having its centre at (?? , -
?? ?? ) & passing through (?? v ?? ,
?? ?? ) 
(C) A parabola with its vertex at (?? , -
?? ?? ) & passing through (?? v ?? ,
?? ?? ) 
(D) None of these 
Ans: (C) v?? 2
+ ?? 2
- ?? = ?? 
? ?? 2
+ ?? 2
= ?? 2
+ 2???? + ?? 2
 
?? 2
= 2?? (?? +
?? 2
) ? Vertex is (0, -
?? 2
) 
It passes through (?? v 2,
?? 2
) 
 
 
Q8: Tangents are drawn from the point ( -?? , ?? ) on the parabola ?? ?? = ?? ?? . The length, these 
tangents will intercept on the line ?? = ?? , is- 
(A) 6 
(B) ?? v ?? 
(C) ?? v ?? 
(D) None 
Ans: (B) Equation of tangent is ?? = ???? +
1
?? ( -1,2) lies on it, then 
2 = -?? +
1
?? ? ?? 2
+ 2?? - 1 = 0
?? = 2, so ?? 1
- ?? 2
= 2( ?? 1
- ?? 2
)+
?? 2
- ?? 1
?? 1
?? 2
 ? ( ?? - ?? 2
)
2
= ( ?? 1
- ?? 2
)
2
(2 -
1
?? 1
?? 2
)
2
 = [( ?? 1
+ ?? 2
)
2
- 4?? 1
?? 2
] (2 -
1
?? 1
?? 2
)
2
 = [( ?? 1
+ ?? 2
)
2
- 4?? 1
?? 2
] (2 -
1
?? 1
?? 2
)
2
( ?? 1
- ?? 2
)
2
= ( 4 + 4) ( 2 + 1)
2
= 8 × 9
 ? |?? 1
- ?? 2
| = 6v 2
 
 
 
 
 
Q9:  Which one of the following equations represented parametric -cally represents equation to a 
parabolic profile? 
(A) ?? = ???????? ?? ; ?? = ???????? ?? 
(B) ?? ?? - ?? = -?????? ?? ; ?? = ?? ?????? ?? 
?? ?? 
(C) v ?? = ?????? ?? ; v?? = ?????? ?? 
(D) ?? = v ?? - ?????? ?? ; ?? = ?????? ?? + ?????? 
?? ?? 
Ans: (B) 
(A) is an ellipse 
 (B) ?? 2
= 2 - cos ?? = 2 - (2cos
2
 
?? 2
- 1) = 2 - (
?? 2
- 1)
 ? ?? 2
=
1
2
( 6 - ?? )
 
? It is a parabola 
(C) is a line in 1
st 
 quadrant 
 (D) ?? = v 1 - sin ?? , ?? = sin 
?? 2
+ cos 
?? 2
 ? ?? 2
= sin
2
 
?? 2
+ cos
2
 
?? 2
+ 2sin 
?? 2
cos 
?? 2
= 1 + sin ?? = 1 + 1 - ?? 2
 (A circle) 
 
 
 
Q10:  From an external point ?? , pair of tangent lines are drawn to the parabola, ?? ?? = ???? . If ?? ?? and 
?? ?? are the inclinations of these tangents with the axis of ?? such that, ?? ?? + ?? ?? =
?? ?? , then the locus 
of ?? is- 
(A) ?? - ?? + ?? = ?? 
(B) ?? + ?? - ?? = ?? 
(C) ?? - ?? - ?? = ?? 
(D) ?? + ?? + ?? = ?? 
Ans: (C) Let A ( ?? ?? 1
2
, 2?? ?? 2
) &?? ( ?? ?? 2
2
, 2?? ?? 2
) be points on parabola. P = ( ?? ?? 1
t
2
'?? ( t
1
+ t
2
) ) = ( x, y) 
slope of ???? is 
1
?? 1
& slope of ???? is 
1
?? 2
 tan ( ?? 1
+ ?? 2
)= 1 
 ?
1
t
1
+
1
t
2
1 -
1
t
1
t
2
= 1
 ?
t
1
+ t
2
t
1
t
2
- 1
= 1
 ?
?? ?? - 1
= 1
 
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