Question

已知a+b+c=0,a^2+b^2+c^2=32,求ab+ac+bc

过程

Answer 1

(a+b+c)² = a²+b²+c²+2ab+2bc+2ac
因此ab+bc+ac = (0²-32)/2 = 16

Answer 2

(a+b+c)^2=a^2+b^2+c^2+2*(ab+bc+ac)=32+2*(ab+bc+ac)=0,所以ab+bc+ac=-16

Answer 3

(a+b+c)² = a²+b²+c²+2ab+2bc+2ac=0
故 ab+bc+ac = (0-32)/2 = -16