NCERT Class XI Mathematics - Conic Sections - Solutions
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Question : 62
Total: 71
Foci (0, ± √ 10 ) , passing through (2, 3).
Solution:
Here foci are (0, ± √ 10 ) which lie on y-axis.
So the equation of hyperbola in standard form is
−
= 1
Now, foci are (0, ±√ 10 ) ⇒ c = √ 10
We know thatc 2 = a 2 + b 2
⇒( √ 10 ) 2 = a 2 + b 2 ⇒ b 2 = 10 - a 2
Since the hyperbola passes through (2, 3)
∴
−
= 1 ⇒
−
= 1
⇒ 9(10 −a 2 ) − 4 a 2 − a 2 ( 10 − a 2 ) = 0
⇒a 4 – 23 a 2 + 90 = 0 ⇒ a 4 – 18 a 2 – 5 a 2 + 90 = 0
⇒ (a 2 – 18)(a 2 – 5) = 0 ⇒ a 2 = 18 or a 2 = 5
Whena 2 = 18 then b 2 = 10 – 18 = –8 (which is not possible)
Whena 2 = 5, then b 2 = 10 – 5 = 5
Thus, required equation of hyperbola is
−
= 1.
So the equation of hyperbola in standard form is
Now, foci are (0, ±
We know that
⇒
Since the hyperbola passes through (2, 3)
∴
⇒ 9(10 −
⇒
⇒ (
When
When
Thus, required equation of hyperbola is
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