美夢成真教甄討論區

a(n)=1-2[a(n-1)]^2, 求 a(n)

- cos(2x) = 1 - 2(cosx)^2
a_0 = - cosx，x = arccos(-a_0)
a_n = - cos(2^n * x) = - cos(2^n * arccos(-a_0))