( )^2 - a^2 - b^2 - c^2 = -2ab-2ac+2bc

问题描述:

( )^2 - a^2 - b^2 - c^2 = -2ab-2ac+2bc

(a-b-c)^2 - a^2 - b^2 - c^2 = -2ab-2ac+2bc