若a+b+c=2,a方+b方+c方=8,则ab+ac+bc=?
问题描述:
若a+b+c=2,a方+b方+c方=8,则ab+ac+bc=?
答
a+b+c=2 (a+b+c) =4a+b+c+2ab+2bc+2ac =4a+b+c =88+2ab+2bc+2ac =4ab+bc+ac=-2
若a+b+c=2,a方+b方+c方=8,则ab+ac+bc=?
a+b+c=2 (a+b+c) =4a+b+c+2ab+2bc+2ac =4a+b+c =88+2ab+2bc+2ac =4ab+bc+ac=-2