∫ ƒ'(x) dx = ∫ [dƒ(x)/dx] dx = ∫ d[ƒ(x)] = ƒ(x) + C嘛这里ƒ'(x) = cosx，ƒ(x) = sinx理所当然∫ d(sinx) = ∫ (sinx)' dx = sinx + C，积分与微分抵消
