The correct option (b) 5 – (4/5)y1
Explanation:
ellipse: (x2/9) + (y2/25) = 1 ⇒ a = 3 and b = 5.
Thus a < b.
∴ Major axis is y axis and two foci lie on y axis.
Their co-ordinates are (0, ± be)
Now e = √[1 – (a2/b2)] = √[1 – (9/25)] = (4/5)
∴ Focus distance of a point (x1, y1) is given by b – ey1 = 5 – (4/5)y1.