sin(x)的1次冪:cos(x)=sin(x+π/2)
sin(x)的2次冪:-sinx=sin(x+2*π/2)
sin(x)的3次冪:-cos(x)=sin(x+3*π/2)
sin(x)的4次冪:sin(x)=sin(x+4*π/2)=sinx
sin(x)的5次冪=sin(x)的1次冪= cos(x)=sin(x+π/2+2π)=sin(x+5*π/2)
……
如此循環(huán)下去可得：
sin(x)的n次冪=sin（x+n*π/2）