设A=X二次方-Xy,B=Xy+Y二次方,求 (1)A+B (2)3a-b
问题描述:
设A=X二次方-Xy,B=Xy+Y二次方,求 (1)A+B (2)3a-b
答
(1)A+B=(X二次方-Xy)+(Xy+Y二次方)
=x²-xy+xy+y²
=x²+y²
(2)3a-b=3(X二次方-Xy)-(Xy+Y二次方)
=3x²-3xy-xy-y²
=3x²-4xy-y²