Let a>0,b>0. Let e and l respectively be the eccentricity and length of the latus rectum of the hyperbola x^2 a^2- y^2 b^2=1. Let e^' and ^'…
JEE Main 2022 — Mathematics Coordinate Geometry
2022mcqmedium
Let a>0,b>0. Let e and l respectively be the eccentricity and length of the latus rectum of the hyperbola a2x2−b2y2=1. Let e′ and l′ respectively the eccentricity and length of the latus rectum of its conjugate hyperbola. If e2=1411l and (e′)2=811l′, then the value of 77a+44b is equal to
Official previous-year question
Held on 28 Jun 2022 · Verified 6 Jul 2026.
Options
A
100
B
110
C
120
D
130
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Solution
By using eccentricty formula we get,
e=1+a2b2,l=a2b2
Given e2=1411l
So, 1+a2b2=1411⋅a2b2
a2a2+b2=711⋅ab2⋯(1)
Also e′=1+b2a2,l′=b2a2
Given (e′)2=811l′
1+b2a2=811⋅b2a2
b2a2+b2=411⋅ba2⋯(2)
Now equation (1)÷equation (2) we get,
a2b2=74⋅a3b3
∴7a=4b⋯(3)
From (2)
b24916b2+b2=411⋅49b16b2
∴b=11×164×65⋯(4)
We have to find value of
77a+44b
So, 11(7a+4b)=11(4b+4b)=11×8b
∴ Value of 11×8b=11×8×16×114×65=130
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