求证(x+y)(x3+y3)≥0
问题描述:
求证(x+y)(x3+y3)≥0
RT
答
(x+y)(x^3+y^3)
=(x+y)(x+y)(x^2-xy+y^2)
=((x+y)^2)((x-y/2)^2+(3y^2)/4)≥0
因为(x+y)^2≥0,(x-y/2)^2+(3y^2)/4≥0