sinx=x-(x^3/3!)+(x^5/5!)-(x^7/7!)+(x^9/9!)-...
令F'(x)=sinx/x=1-(x^2/3!)+(x^4/5!)-(x^6/7!)+(x^8/9!)-...
则F(x)=x-(x^3/3!3)+(x^5/5!5)-(x^7/7!7)+(x^9/9!9)-...
实际取项应达所需精度显然F(x)不是初等函数