Let the asymptote be y=2x, which is simultaneous with the equation of C 1, and x 2 = a 2 * b 2/(4a 2+b 2) is obtained.

Combining the circle x 2+y 2 = a 2, x' 2 = a 2/5 is obtained.

|x|=|x'|/3, so | x | 2 = | x' | 2/9.

Substitute A 2 = B 2+5 to get C.