.求多项式3x2+y2-5xy与-4xy-y2+7x2的和. 问题详情:.求多项式3x2+y2-5xy与-4xy-y2+7x2的和.【回答】(3x2+y2-5xy)+(-4xy-y2+7x2)=10x2-9xy;知识点:整式的加减题型:计算题...