A=x^2-xy,B=xy+y^2,则A+B=___,A-B=___,3A-2B=___.

问题描述:

A=x^2-xy,B=xy+y^2,则A+B=___,A-B=___,3A-2B=___.

A+B=x²+y²
A-B=x²-2xy-y²
3A-2B=3x²-5xy-2y