根据泰勒展开：sin x = x-x^3/3!+x^5/5!-……+(-1)^(k-1)*(x^(2k-1))/(2k-1)!+……。(-∞cos x = 1-x^2/2!+x^4/4!-……+(-1)k*(x^(2k))/(2k)!+…… (-∞最后tanx=sinx/cosx
