因式分解:ab - ac - b^2 + 2bc - c^2 =
问题描述：
因式分解:ab - ac - b^2 + 2bc - c^2 =
答
ab - ac - b^2 + 2bc - c^2
=a(b-c)-(b^2-2bc+c^2)
=a(b-c)-(b-c)^2
=(b-c)(a-b+c)