AP EAMCET2015MathematicsHyperbola
The foci of the ellipse x^2 16 + y^2 b^2 =1 and the hyperbola x^2 144 - y^2 81 = 1 25 coincide. Then, the value of b^2 is
Options
- A5
- B7
- C9
- D1
Correct answer
B. 7
Step-by-step solution
Equation of ellipse, x^2 16 + y^2 b^2 =1 Eccentricity, e= 1- b^2 16 = 16-b^2 4 So, the focus will be ( 16-b^2 , 0 ) Also, the equation of hyperbola, x^2 144 - y^2 81 = 1 25 x^2 ( 144 25 ) - y^2 ( 81 25 ) =1 e= 1+ b^2 a^2 = 1+ 81 25 144 25 = 15 12 So, the focus will be ( 12 5 15 12 , 0 ) i.e., ( 3,0) On comparing the focus of ellipse with hyperbola, we get aligned & 16-b^2 =3 & 16-b^2=9 & b^2=7 aligned