ƒ(x)的原函数为(lnx)²==> ∫ ƒ(x) dx = (lnx)²==> ƒ(x) = 2(lnx)(1/x) = (2/x)(lnx)∫ xƒ'(x) dx= ∫ x d[ƒ(x)]= xƒ(x) - ∫ ƒ(x) dx= x(2/x)(lnx) - (lnx)²= 2lnx - (lnx)²
