[VA] Short & Sweet Math Challenge #24: "2019 Spring Special 5-tier"

[Albert Chan]

Perhaps cin(x) need a bit more restriction, not just cin(cin(cin(x))) = sin(x)

sin(cin(x)) = cin(sin(x))

cin(x) should be an odd function, shape like sin(x), with value between sin(x) and x

For domain [-pi/2, pi/2], cin(x) ≈ (1 + x²/9) sin(x)

Example:

sin(½) = 0.4794255386
cin(cin(cin(½))) = 0.4791650974, relative error ~ -0.05%

sin(cin(½)) ≈ 0.473044
cin(sin(½)) ≈ 0.473050