问题描述: 已知实数x,y满足x*2+xy+y*2=3,x+2y的最大值? 1个回答 分类:数学 2014-10-04 问题解答: 我来补答 x^2+xy+y^2=3设t=x+2yx=t-2y(t-2y)^2+(t-2Y)y+y^2=3t^2-4yt+4y^2+ty-2y^2+y^2=33y^2-(4t-t)y+t^2-3=03y^2-(3t)y+t^2-3=0deta>=09t^2-12(t^2-3)>=0-3t^2+36>=0t^2 展开全文阅读