Page 1
Solved Examples on Hyperbola
Q1: The equation of the conic with focus at (?? , -?? ), directrix along ?? - ?? +
?? = ?? and with eccentricity v ?? is
(a) ?? ?? - ?? ?? = ??
(b) ???? = ??
(c) ?? ???? - ?? ?? + ?? ?? + ?? = ??
(d) ?? ???? + ?? ?? - ?? ?? - ?? = ??
Ans: (c)
Sol: Here, focus (?? ) = (1, -1), eccentricity (?? ) = v 2
From definition, ???? = ??????
v(?? - 1)
2
+ (?? + 1)
2
=
v 2 · (?? - ?? + 1)
v1
2
+ 1
2
? (?? - 1)
2
+ (?? + 1)
2
= (?? - ?? + 1)
2
? 2???? - 4?? + 4?? + 1 = 0, which is the
required equation of conic (Rectangular hyperbola)
Q2: If the foci of the ellipse
?? ?? ????
+
?? ?? ?? ?? = ?? and the hyperbola
?? ?? ??????
-
?? ?? ????
=
?? ????
coincide, then the value of ?? ?? is
(a) 1
(b) 5
(c) 7
(d) 9
Ans: (c)
Sol:
For hyperbola,
?? 2
144
-
?? 2
81
=
1
25
?? =
v
144
25
, ?? =
v
81
25
, ?? 1
=
v
1 +
?? 2
?? 2
=
v
1 +
81
144
=
v
225
144
=
5
4
Therefore foci = (±?? ?? 1
, 0) = (±
12
5
·
5
4
, 0) = (±3,0). Therefore foci of ellipse i.e.,
(±4?? , 0) = (±3,0) (For ellipse ?? = 4) ? ?? =
3
4
, Hence ?? 2
= 16(1 -
9
16
) = 7.
Page 2
Solved Examples on Hyperbola
Q1: The equation of the conic with focus at (?? , -?? ), directrix along ?? - ?? +
?? = ?? and with eccentricity v ?? is
(a) ?? ?? - ?? ?? = ??
(b) ???? = ??
(c) ?? ???? - ?? ?? + ?? ?? + ?? = ??
(d) ?? ???? + ?? ?? - ?? ?? - ?? = ??
Ans: (c)
Sol: Here, focus (?? ) = (1, -1), eccentricity (?? ) = v 2
From definition, ???? = ??????
v(?? - 1)
2
+ (?? + 1)
2
=
v 2 · (?? - ?? + 1)
v1
2
+ 1
2
? (?? - 1)
2
+ (?? + 1)
2
= (?? - ?? + 1)
2
? 2???? - 4?? + 4?? + 1 = 0, which is the
required equation of conic (Rectangular hyperbola)
Q2: If the foci of the ellipse
?? ?? ????
+
?? ?? ?? ?? = ?? and the hyperbola
?? ?? ??????
-
?? ?? ????
=
?? ????
coincide, then the value of ?? ?? is
(a) 1
(b) 5
(c) 7
(d) 9
Ans: (c)
Sol:
For hyperbola,
?? 2
144
-
?? 2
81
=
1
25
?? =
v
144
25
, ?? =
v
81
25
, ?? 1
=
v
1 +
?? 2
?? 2
=
v
1 +
81
144
=
v
225
144
=
5
4
Therefore foci = (±?? ?? 1
, 0) = (±
12
5
·
5
4
, 0) = (±3,0). Therefore foci of ellipse i.e.,
(±4?? , 0) = (±3,0) (For ellipse ?? = 4) ? ?? =
3
4
, Hence ?? 2
= 16(1 -
9
16
) = 7.
Q3: If ???? is a double ordinate of hyperbola
?? ?? ?? ?? -
?? ?? ?? ?? = ?? such that ?????? is an
equilateral triangle, ?? being the centre of the hyperbola. Then the
eccentricity ?? of the hyperbola satisfies
(a) ?? < ?? < ?? /v ??
(b) ?? = ?? /v ??
(c) ?? = v ?? /??
(d) ?? > ?? /v ??
Ans: (d)
Sol:
Let ?? (?? sec ?? , ?? tan ?? ); ?? (?? sec ?? , -?? tan ?? ) be end points of double ordinates and
?? (0,0) is the centre of the hyperbola
Now ???? = 2?? tan ?? ; ???? = ???? = v?? 2
sec
2
?? + ?? 2
tan
2
??
Since ???? = ???? = ???? , ? 4?? 2
tan
2
?? = ?? 2
sec
2
?? + ?? 2
tan
2
??
? 3?? 2
tan
2
?? = ?? 2
sec
2
?? ? 3?? 2
sin
2
?? = ?? 2
? 3?? 2
(?? 2
- 1)sin
2
?? = ?? 2
= 3(?? 2
- 1)sin
2
?? = 1
?
1
3(?? 2
- 1)
= sin
2
?? < 1 (? sin
2
?? < 1)
?
1
?? 2
- 1
< 3 ? ?? 2
- 1 >
1
3
= ?? 2
>
4
3
? ?? >
2
v 3
Q4: The eccentricity of the conjugate hyperbola of the hyperbola ?? ?? - ?? ?? ?? =
?? , is
(a) 2
(b)
?? v ??
(c) 4
Page 3
Solved Examples on Hyperbola
Q1: The equation of the conic with focus at (?? , -?? ), directrix along ?? - ?? +
?? = ?? and with eccentricity v ?? is
(a) ?? ?? - ?? ?? = ??
(b) ???? = ??
(c) ?? ???? - ?? ?? + ?? ?? + ?? = ??
(d) ?? ???? + ?? ?? - ?? ?? - ?? = ??
Ans: (c)
Sol: Here, focus (?? ) = (1, -1), eccentricity (?? ) = v 2
From definition, ???? = ??????
v(?? - 1)
2
+ (?? + 1)
2
=
v 2 · (?? - ?? + 1)
v1
2
+ 1
2
? (?? - 1)
2
+ (?? + 1)
2
= (?? - ?? + 1)
2
? 2???? - 4?? + 4?? + 1 = 0, which is the
required equation of conic (Rectangular hyperbola)
Q2: If the foci of the ellipse
?? ?? ????
+
?? ?? ?? ?? = ?? and the hyperbola
?? ?? ??????
-
?? ?? ????
=
?? ????
coincide, then the value of ?? ?? is
(a) 1
(b) 5
(c) 7
(d) 9
Ans: (c)
Sol:
For hyperbola,
?? 2
144
-
?? 2
81
=
1
25
?? =
v
144
25
, ?? =
v
81
25
, ?? 1
=
v
1 +
?? 2
?? 2
=
v
1 +
81
144
=
v
225
144
=
5
4
Therefore foci = (±?? ?? 1
, 0) = (±
12
5
·
5
4
, 0) = (±3,0). Therefore foci of ellipse i.e.,
(±4?? , 0) = (±3,0) (For ellipse ?? = 4) ? ?? =
3
4
, Hence ?? 2
= 16(1 -
9
16
) = 7.
Q3: If ???? is a double ordinate of hyperbola
?? ?? ?? ?? -
?? ?? ?? ?? = ?? such that ?????? is an
equilateral triangle, ?? being the centre of the hyperbola. Then the
eccentricity ?? of the hyperbola satisfies
(a) ?? < ?? < ?? /v ??
(b) ?? = ?? /v ??
(c) ?? = v ?? /??
(d) ?? > ?? /v ??
Ans: (d)
Sol:
Let ?? (?? sec ?? , ?? tan ?? ); ?? (?? sec ?? , -?? tan ?? ) be end points of double ordinates and
?? (0,0) is the centre of the hyperbola
Now ???? = 2?? tan ?? ; ???? = ???? = v?? 2
sec
2
?? + ?? 2
tan
2
??
Since ???? = ???? = ???? , ? 4?? 2
tan
2
?? = ?? 2
sec
2
?? + ?? 2
tan
2
??
? 3?? 2
tan
2
?? = ?? 2
sec
2
?? ? 3?? 2
sin
2
?? = ?? 2
? 3?? 2
(?? 2
- 1)sin
2
?? = ?? 2
= 3(?? 2
- 1)sin
2
?? = 1
?
1
3(?? 2
- 1)
= sin
2
?? < 1 (? sin
2
?? < 1)
?
1
?? 2
- 1
< 3 ? ?? 2
- 1 >
1
3
= ?? 2
>
4
3
? ?? >
2
v 3
Q4: The eccentricity of the conjugate hyperbola of the hyperbola ?? ?? - ?? ?? ?? =
?? , is
(a) 2
(b)
?? v ??
(c) 4
(d)
?? ??
Ans: (a)
Sol: The given hyperbola is
?? 2
1
-
?? 2
1/3
= 1. Here ?? 2
= 1 and ?? 2
=
1
3
Since ?? 2
= ?? 2
(?? 2
- 1) ?
1
3
= 1(?? 2
- 1) ? ?? 2
=
4
3
? ?? =
2
v 3
If ?? '
is the eccentricity of the conjugate hyperbola, then
1
?? 2
+
1
?? '2
= 1 ?
1
?? '2
= 1 -
1
?? 2
= 1 -
3
4
=
1
4
? ?? '
= 2.
Q5:The distance between the directrices of the hyperbola ?? = ???????? ?? , ?? =
???????? ?? is
(a) ???? v ??
(b) v ??
(c) ?? v ??
(d) ?? , v ??
Ans: (c)
Sol: Equation of hyperbola is ?? = 8sec ?? , ?? = 8tan ?? ?
?? 8
= sec ?? ,
?? 8
= tan ??
? sec
2
?? - tan
2
?? = 1 ?
?? 2
8
2
-
?? 2
8
2
= 1
Here ?? = 8, ?? = 8. Now ?? = v1 +
?? 2
?? 2
= v1 +
8
2
8
2
= v 2
? Distance between directrices =
2?? ?? =
2×8
v 2
= 8v 2.
Q6: If ?? ?? and ?? ?? are the slopes of the tangents to the hyperbola
?? ?? ????
-
?? ?? ????
= ??
which pass through the point (?? , ?? ), then
(a) ?? ?? + ?? ?? =
????
????
(b) ?? ?? ?? ?? =
????
????
(c) ?? ?? + ?? ?? =
????
????
(d) ?? ?? ?? ?? =
????
????
Ans: (a, b)
Page 4
Solved Examples on Hyperbola
Q1: The equation of the conic with focus at (?? , -?? ), directrix along ?? - ?? +
?? = ?? and with eccentricity v ?? is
(a) ?? ?? - ?? ?? = ??
(b) ???? = ??
(c) ?? ???? - ?? ?? + ?? ?? + ?? = ??
(d) ?? ???? + ?? ?? - ?? ?? - ?? = ??
Ans: (c)
Sol: Here, focus (?? ) = (1, -1), eccentricity (?? ) = v 2
From definition, ???? = ??????
v(?? - 1)
2
+ (?? + 1)
2
=
v 2 · (?? - ?? + 1)
v1
2
+ 1
2
? (?? - 1)
2
+ (?? + 1)
2
= (?? - ?? + 1)
2
? 2???? - 4?? + 4?? + 1 = 0, which is the
required equation of conic (Rectangular hyperbola)
Q2: If the foci of the ellipse
?? ?? ????
+
?? ?? ?? ?? = ?? and the hyperbola
?? ?? ??????
-
?? ?? ????
=
?? ????
coincide, then the value of ?? ?? is
(a) 1
(b) 5
(c) 7
(d) 9
Ans: (c)
Sol:
For hyperbola,
?? 2
144
-
?? 2
81
=
1
25
?? =
v
144
25
, ?? =
v
81
25
, ?? 1
=
v
1 +
?? 2
?? 2
=
v
1 +
81
144
=
v
225
144
=
5
4
Therefore foci = (±?? ?? 1
, 0) = (±
12
5
·
5
4
, 0) = (±3,0). Therefore foci of ellipse i.e.,
(±4?? , 0) = (±3,0) (For ellipse ?? = 4) ? ?? =
3
4
, Hence ?? 2
= 16(1 -
9
16
) = 7.
Q3: If ???? is a double ordinate of hyperbola
?? ?? ?? ?? -
?? ?? ?? ?? = ?? such that ?????? is an
equilateral triangle, ?? being the centre of the hyperbola. Then the
eccentricity ?? of the hyperbola satisfies
(a) ?? < ?? < ?? /v ??
(b) ?? = ?? /v ??
(c) ?? = v ?? /??
(d) ?? > ?? /v ??
Ans: (d)
Sol:
Let ?? (?? sec ?? , ?? tan ?? ); ?? (?? sec ?? , -?? tan ?? ) be end points of double ordinates and
?? (0,0) is the centre of the hyperbola
Now ???? = 2?? tan ?? ; ???? = ???? = v?? 2
sec
2
?? + ?? 2
tan
2
??
Since ???? = ???? = ???? , ? 4?? 2
tan
2
?? = ?? 2
sec
2
?? + ?? 2
tan
2
??
? 3?? 2
tan
2
?? = ?? 2
sec
2
?? ? 3?? 2
sin
2
?? = ?? 2
? 3?? 2
(?? 2
- 1)sin
2
?? = ?? 2
= 3(?? 2
- 1)sin
2
?? = 1
?
1
3(?? 2
- 1)
= sin
2
?? < 1 (? sin
2
?? < 1)
?
1
?? 2
- 1
< 3 ? ?? 2
- 1 >
1
3
= ?? 2
>
4
3
? ?? >
2
v 3
Q4: The eccentricity of the conjugate hyperbola of the hyperbola ?? ?? - ?? ?? ?? =
?? , is
(a) 2
(b)
?? v ??
(c) 4
(d)
?? ??
Ans: (a)
Sol: The given hyperbola is
?? 2
1
-
?? 2
1/3
= 1. Here ?? 2
= 1 and ?? 2
=
1
3
Since ?? 2
= ?? 2
(?? 2
- 1) ?
1
3
= 1(?? 2
- 1) ? ?? 2
=
4
3
? ?? =
2
v 3
If ?? '
is the eccentricity of the conjugate hyperbola, then
1
?? 2
+
1
?? '2
= 1 ?
1
?? '2
= 1 -
1
?? 2
= 1 -
3
4
=
1
4
? ?? '
= 2.
Q5:The distance between the directrices of the hyperbola ?? = ???????? ?? , ?? =
???????? ?? is
(a) ???? v ??
(b) v ??
(c) ?? v ??
(d) ?? , v ??
Ans: (c)
Sol: Equation of hyperbola is ?? = 8sec ?? , ?? = 8tan ?? ?
?? 8
= sec ?? ,
?? 8
= tan ??
? sec
2
?? - tan
2
?? = 1 ?
?? 2
8
2
-
?? 2
8
2
= 1
Here ?? = 8, ?? = 8. Now ?? = v1 +
?? 2
?? 2
= v1 +
8
2
8
2
= v 2
? Distance between directrices =
2?? ?? =
2×8
v 2
= 8v 2.
Q6: If ?? ?? and ?? ?? are the slopes of the tangents to the hyperbola
?? ?? ????
-
?? ?? ????
= ??
which pass through the point (?? , ?? ), then
(a) ?? ?? + ?? ?? =
????
????
(b) ?? ?? ?? ?? =
????
????
(c) ?? ?? + ?? ?? =
????
????
(d) ?? ?? ?? ?? =
????
????
Ans: (a, b)
Sol: The line through (6,2) is ?? - 2 = ?? (?? - 6) ? ?? = ???? + 2 - 6??
Now, from condition of tangency (2 - 6?? )
2
= 25?? 2
- 16
? 36?? 2
+ 4 - 24?? - 25?? 2
+ 16 = 0 ? 11?? 2
- 24?? + 20 = 0
Obviously, its roots are ?? 1
and ?? 2
, therefore ?? 1
+ ?? 2
=
24
11
and ?? 1
?? 2
=
20
11
Q7: If the tangent at the point (???????? ?? , ???????? ?? ) on the hyperbola
?? ?? ?? -
?? ?? ?? = ?? is
parallel to ?? ?? - ?? + ?? = ?? , then the value of ?? is
(a) ????
°
(b) ????
°
(c) ????
°
(d) ????
°
Ans: (c)
Sol: Here ?? = 2sec ?? and ?? = 3tan ??
Differentiating w.r.t. ??
????
????
= 2sec ?? tan ?? and
????
????
= 3sec
2
??
? Gradient of tangent
????
????
=
???? /????
???? /????
=
3sec
2
?? 2sec ?? tan ?? ; ?
????
????
=
3
2
cosec ??
But tangent is parallel to 3?? - ?? + 4 = 0; ? Gradient ?? = 3
From (i) and (ii),
3
2
cosec ?? = 3 ? cosec ?? = 2, ? ?? = 30
°
Q8: The locus of the point of intersection of tangents to the hyperbola
?? ?? ?? - ?? ?? ?? = ???? which meet at a constant angle ?? /?? , is
(a) (?? ?? + ?? ?? - ?? )
?? = ?? (?? ?? ?? - ?? ?? ?? + ???? )
(b) (?? ?? + ?? ?? - ?? ) = ?? (?? ?? ?? - ?? ?? ?? + ???? )
(c) ?? (?? ?? + ?? ?? - ?? )
?? = (?? ?? ?? - ?? ?? ?? + ???? )
(d) None of these
Ans: (a)
Sol: Let the point of intersection of tangents be ?? (?? 1
, ?? 1
). Then the equation of
pair of tangents from ?? (?? 1
, ?? 1
) to the given hyperbola is (4?? 2
- 9?? 2
- 36)(4?? 1
2
-
9?? 1
2
- 36) = [4?? 1
?? - 9?? 1
?? - 36]
2
Page 5
Solved Examples on Hyperbola
Q1: The equation of the conic with focus at (?? , -?? ), directrix along ?? - ?? +
?? = ?? and with eccentricity v ?? is
(a) ?? ?? - ?? ?? = ??
(b) ???? = ??
(c) ?? ???? - ?? ?? + ?? ?? + ?? = ??
(d) ?? ???? + ?? ?? - ?? ?? - ?? = ??
Ans: (c)
Sol: Here, focus (?? ) = (1, -1), eccentricity (?? ) = v 2
From definition, ???? = ??????
v(?? - 1)
2
+ (?? + 1)
2
=
v 2 · (?? - ?? + 1)
v1
2
+ 1
2
? (?? - 1)
2
+ (?? + 1)
2
= (?? - ?? + 1)
2
? 2???? - 4?? + 4?? + 1 = 0, which is the
required equation of conic (Rectangular hyperbola)
Q2: If the foci of the ellipse
?? ?? ????
+
?? ?? ?? ?? = ?? and the hyperbola
?? ?? ??????
-
?? ?? ????
=
?? ????
coincide, then the value of ?? ?? is
(a) 1
(b) 5
(c) 7
(d) 9
Ans: (c)
Sol:
For hyperbola,
?? 2
144
-
?? 2
81
=
1
25
?? =
v
144
25
, ?? =
v
81
25
, ?? 1
=
v
1 +
?? 2
?? 2
=
v
1 +
81
144
=
v
225
144
=
5
4
Therefore foci = (±?? ?? 1
, 0) = (±
12
5
·
5
4
, 0) = (±3,0). Therefore foci of ellipse i.e.,
(±4?? , 0) = (±3,0) (For ellipse ?? = 4) ? ?? =
3
4
, Hence ?? 2
= 16(1 -
9
16
) = 7.
Q3: If ???? is a double ordinate of hyperbola
?? ?? ?? ?? -
?? ?? ?? ?? = ?? such that ?????? is an
equilateral triangle, ?? being the centre of the hyperbola. Then the
eccentricity ?? of the hyperbola satisfies
(a) ?? < ?? < ?? /v ??
(b) ?? = ?? /v ??
(c) ?? = v ?? /??
(d) ?? > ?? /v ??
Ans: (d)
Sol:
Let ?? (?? sec ?? , ?? tan ?? ); ?? (?? sec ?? , -?? tan ?? ) be end points of double ordinates and
?? (0,0) is the centre of the hyperbola
Now ???? = 2?? tan ?? ; ???? = ???? = v?? 2
sec
2
?? + ?? 2
tan
2
??
Since ???? = ???? = ???? , ? 4?? 2
tan
2
?? = ?? 2
sec
2
?? + ?? 2
tan
2
??
? 3?? 2
tan
2
?? = ?? 2
sec
2
?? ? 3?? 2
sin
2
?? = ?? 2
? 3?? 2
(?? 2
- 1)sin
2
?? = ?? 2
= 3(?? 2
- 1)sin
2
?? = 1
?
1
3(?? 2
- 1)
= sin
2
?? < 1 (? sin
2
?? < 1)
?
1
?? 2
- 1
< 3 ? ?? 2
- 1 >
1
3
= ?? 2
>
4
3
? ?? >
2
v 3
Q4: The eccentricity of the conjugate hyperbola of the hyperbola ?? ?? - ?? ?? ?? =
?? , is
(a) 2
(b)
?? v ??
(c) 4
(d)
?? ??
Ans: (a)
Sol: The given hyperbola is
?? 2
1
-
?? 2
1/3
= 1. Here ?? 2
= 1 and ?? 2
=
1
3
Since ?? 2
= ?? 2
(?? 2
- 1) ?
1
3
= 1(?? 2
- 1) ? ?? 2
=
4
3
? ?? =
2
v 3
If ?? '
is the eccentricity of the conjugate hyperbola, then
1
?? 2
+
1
?? '2
= 1 ?
1
?? '2
= 1 -
1
?? 2
= 1 -
3
4
=
1
4
? ?? '
= 2.
Q5:The distance between the directrices of the hyperbola ?? = ???????? ?? , ?? =
???????? ?? is
(a) ???? v ??
(b) v ??
(c) ?? v ??
(d) ?? , v ??
Ans: (c)
Sol: Equation of hyperbola is ?? = 8sec ?? , ?? = 8tan ?? ?
?? 8
= sec ?? ,
?? 8
= tan ??
? sec
2
?? - tan
2
?? = 1 ?
?? 2
8
2
-
?? 2
8
2
= 1
Here ?? = 8, ?? = 8. Now ?? = v1 +
?? 2
?? 2
= v1 +
8
2
8
2
= v 2
? Distance between directrices =
2?? ?? =
2×8
v 2
= 8v 2.
Q6: If ?? ?? and ?? ?? are the slopes of the tangents to the hyperbola
?? ?? ????
-
?? ?? ????
= ??
which pass through the point (?? , ?? ), then
(a) ?? ?? + ?? ?? =
????
????
(b) ?? ?? ?? ?? =
????
????
(c) ?? ?? + ?? ?? =
????
????
(d) ?? ?? ?? ?? =
????
????
Ans: (a, b)
Sol: The line through (6,2) is ?? - 2 = ?? (?? - 6) ? ?? = ???? + 2 - 6??
Now, from condition of tangency (2 - 6?? )
2
= 25?? 2
- 16
? 36?? 2
+ 4 - 24?? - 25?? 2
+ 16 = 0 ? 11?? 2
- 24?? + 20 = 0
Obviously, its roots are ?? 1
and ?? 2
, therefore ?? 1
+ ?? 2
=
24
11
and ?? 1
?? 2
=
20
11
Q7: If the tangent at the point (???????? ?? , ???????? ?? ) on the hyperbola
?? ?? ?? -
?? ?? ?? = ?? is
parallel to ?? ?? - ?? + ?? = ?? , then the value of ?? is
(a) ????
°
(b) ????
°
(c) ????
°
(d) ????
°
Ans: (c)
Sol: Here ?? = 2sec ?? and ?? = 3tan ??
Differentiating w.r.t. ??
????
????
= 2sec ?? tan ?? and
????
????
= 3sec
2
??
? Gradient of tangent
????
????
=
???? /????
???? /????
=
3sec
2
?? 2sec ?? tan ?? ; ?
????
????
=
3
2
cosec ??
But tangent is parallel to 3?? - ?? + 4 = 0; ? Gradient ?? = 3
From (i) and (ii),
3
2
cosec ?? = 3 ? cosec ?? = 2, ? ?? = 30
°
Q8: The locus of the point of intersection of tangents to the hyperbola
?? ?? ?? - ?? ?? ?? = ???? which meet at a constant angle ?? /?? , is
(a) (?? ?? + ?? ?? - ?? )
?? = ?? (?? ?? ?? - ?? ?? ?? + ???? )
(b) (?? ?? + ?? ?? - ?? ) = ?? (?? ?? ?? - ?? ?? ?? + ???? )
(c) ?? (?? ?? + ?? ?? - ?? )
?? = (?? ?? ?? - ?? ?? ?? + ???? )
(d) None of these
Ans: (a)
Sol: Let the point of intersection of tangents be ?? (?? 1
, ?? 1
). Then the equation of
pair of tangents from ?? (?? 1
, ?? 1
) to the given hyperbola is (4?? 2
- 9?? 2
- 36)(4?? 1
2
-
9?? 1
2
- 36) = [4?? 1
?? - 9?? 1
?? - 36]
2
From ?? ?? 1
= ?? 2
or ?? 2
(?? 1
2
+ 4) + 2?? 1
?? 1
???? + ?? 2
(?? 1
2
- 9) + ? . = 0
Since angle between the tangents is ?? /4.
? tan (?? /4) =
2v[?? 1
2
?? 1
2
-(?? 1
2
+4)(?? 1
2
-9)]
?? 1
2
+4+?? 1
2
-9
. Hence locus of ?? (?? 1
, ?? 1
) is (?? 2
+ ?? 2
- 5)
2
=
4(9?? 2
- 4?? 2
+ 36).
Q9: The locus of the mid-points of the chords of the circle ?? ?? + ?? ?? = ????
which are tangent to the hyperbola ?? ?? ?? - ???? ?? ?? = ?????? is
(a) (?? ?? + ?? ?? )
?? = ???? ?? ?? - ?? ?? ??
(b) (?? ?? + ?? ?? )
?? = ?? ?? ?? - ???? ?? ??
(c) (?? ?? - ?? ?? )
?? = ???? ?? ?? - ?? ?? ??
(d) None of these
Ans: (a)
Sol: The given hyperbola is
?? 2
16
-
?? 2
9
= 1
Any tangent to (i) is ?? = ???? + v16?? 2
- 9
Let (?? 1
, ?? 1
) be the mid point of the chord of the circle ?? 2
+ ?? 2
= 16
Then equation of the chord is ?? = ?? 1
i.e., ?? ?? 1
+ ?? ?? 1
- (?? 1
2
+ ?? 1
2
) = 0
Since (ii) and (iii) represent the same line.
?
?? ?? 1
=
-1
?? 1
=
v16?? 2
- 9
-(?? 1
2
+ ?? 1
2
)
? ?? = -
?? 1
?? 1
and (?? 1
2
+ ?? 1
2
)
2
= ?? 1
2
(16?? 2
- 9) ? (?? 1
2
+ ?? 1
2
)
2
= 16 ·
?? 1
2
?? 1
2
?? 1
2
- 9?? 1
2
=
16?? 1
2
- 9?? 1
2
? Locus of (?? 1
, ?? 1
) is (?? 2
+ ?? 2
)
2
= 16?? 2
- 9?? 2
.
Q10: From any point on the hyperbola,
?? ?? ?? ?? -
?? ?? ?? ?? = ?? tangents are drawn to the
hyperbola
?? ?? ?? ?? -
?? ?? ?? ?? = ?? . The area cut-off by the chord of contact on the
asymptotes is equal to
(a)
????
??
(b) ????
(c) ?? ????
Read More