To this end, we first use x > on (0, π/2). Arctanx (self-proof) relation is calibrated if it can be proved as Arctanx >; π/2 (n+ 1) can be used to get a [n-1] = 2a [n]/(1-a [n] 2), and we can see the formula of twice the tangent, so we might as well set a [n] = tan (θ arctan (a).

This topic is not easy to do. . . . It's very strange and hard, please adopt it. . .