(a+b+c)^2=?

问题描述:

(a+b+c)^2=?
注:(a+b+c)^2意为a+b+c括号的平方.

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