(sinx)^2=(1-cos2x)/2而cos2x=1-(2x)^2/2!+(2x)^4/4!-(2x)^6/6!+...., 收敛域为R故(sinx)^2=1/2[4x^2/2!-2^4x^4/4!+2^6x^6/6!-..]=x^2-2^3x^4/4!+2^5x^6/6!-....
