用级数求 cosx=1-(x^2)/(2!)+(x^4)/(4!)-(x^6)/(6!)+...(-1)^n*x^(2n) /((2n)!) x属于（负无穷,正无穷） sinx=x-(x^3)/(3!)+(x^5)/(5!)-(x^7)/(7!)+...(-1)^n*x^(2n+1) /((2n+1)!) x属于（n+1负无穷,正无穷）
