晕,
sinx 单增[-π/2+kπ,π/2+kπ],单减[π/2+kπ,π/2+(k+1)π],
cosx 单增[-π+kπ,kπ],单减[kπ,(k+1)π],
tanx 单增[-π/2+kπ,π/2+kπ],