Let E1 : x29 + y24 = 1 be an ellipse. Ellipses Ei's are constructed such that their centres and eccentricities are same as that of E1, and the length of minor axis of Ei is the length of major axis of Ei+1 (i 1). If Ai is the area of the ellipse Ei, then 5 ( i=1 Ai ), is equal to .
Answer
54
Solution
E1: a1 = 3, b1 = 2 A1 = a1 b1 = 6
Same eccentricity biai = 23 for every i.
ai+1 = bi = 23ai and bi+1 = 23ai+1 = 23bi
Ai+1Ai = ( 23 )2 = 49
i=1 Ai = 6 1 - 49 = 54 5
5 i=1 Ai = 54
Answer: 54