即係一定要拆咗fractions先至sub u=x-1? 如果我未拆就sub會出: ∫(u^(2)-1)/u^(2)du = ∫1-(1/u^(2))du = u + 1/u + C = (x-1) + 1/(x-1) + C 但正確答案係 x + 1/(x-1) + C