求導數
g(t)=tan(arcsint)
g'(t)=sec^2(arcsint) .(arcsint)'
=sec^2(arcsint) .1/√(1-t^2)
(1) tan(arcsin(t)) = sin(arcsin(t))/cos(arcsin(t)) = t/√(1-t^2)
Note: arcsin(t) 的 range 是 [-π/2,π/2]. 在此範圍 cos 值非負.
(2) sec^2(arcsin(t)) = 1/cos^2(arcsin(t)) = 1/[1-sin^2(arcsin(t))] = 1/(1-t^2)