tan(arctanx)=x (x∈R)
sin(arcsinx)=x (-1<=x<=1)
cos(arccosx)=x (-1<=x<=1)
sin(arccosx)=√1-x^2 (-1<=x<=1)
cos(arcsinx)=√1-x^2 (-1<=x<=1)
设t=arccosx，则求sin（arccosx）就是求sint。
由t=arccosx，有：x=cost，所以sint=√(1-cos²t)=√(1-x²)。
sin(arc cosv)=√(1-v^2)
sin(4arc cos(x/2))=4√(1-(x/2)^2)
arcsin(sinx)=x (-π/2<=x<=π/2)
arccos(cosx)=x (-π/2<=x<=π/2)
arctan(tanx)=x (-π/2<x<π/2)