因为 ABC = 1,所以：1 + B + BC = ABC + B + BC = B (1 + C + AC)1 + A + AB = ABC + A + AB = A (1 + B + BC) = AB (1 + C + AC)所以：X/(1 + A + AB) + X/(1 + B + BC) + X/(1 + C + AC)= X/[AB(1 + C + AC)] + X/...