Let a > 0 ,   b > 0 . Let e and l respectively be the eccentricity and length of the latus…

Let a>0, b>0. Let e and l respectively be the eccentricity and length of the latus rectum of the hyperbola x2a2-y2b2=1. Let e' and l' respectively the eccentricity and length of the latus rectum of its conjugate hyperbola. If e2=1114l and e'2=118l', then the value of 77a+44b is equal to
  1. 100
  2. 110
  3. 120
  4. 130

Solution

By using eccentricty formula we get,

e=1+b2a2,l=2b2a

Given e2=1114l

So, 1+b2a2=1114·2b2a

a2+b2a2=117·b2a     1

Also e'=1+a2 b2,l'=2a2 b

Given e'2=118l'

1+a2b2=118·2a2b

a2+b2b2=114·a2b     2

Now equation 1÷equation 2 we get,

b2a2=47·b3a3

7a=4b     3

From 2

16b249+b2b2=114·16b249b

 b=4×6511×16      4

We have to find value of

77a+44b

So, 117a+4b=114b+4b=11×8b

 Value of 11×8b=11×8×4×6516×11=130

Asked in: JEE Main 2022 (28 Jun Shift 2)

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