Question

If P(π/4) is any point on the ellipse 9x² + 25y² = 225, S and S’ are its foci, then SP . S’P = ________

(A) 13 

(B) 14 

(C) 17 

(D) 19

Answer 1

Correct option is: (C) 17

9x² + 25y² = 225

\(\frac {x^2}{25} - \frac {y^2}{9} = 1\)

Here, a = 5, b = 3 

Eccentricity (e) = 4/5

 ∴ a/e = \(\frac {5}{\frac {4}{5}} \)= 25/4

Coordinates of foci are S(4, 0) and S'(-4, 0)

P(θ) = (a cos θ, b sin θ)