设A=x的平方—xy,B=xy+y的平方,求.A+B还有3A—B.
问题描述:
设A=x的平方—xy,B=xy+y的平方,求.A+B还有3A—B.
答
A=x²-xy
B=xy+y²
A+B
=x²-xy+xy+y²
=x²+y²
3A-B
=3(x²-xy)-(xy+y²)
=3x²-3xy-xy-y²
=3x²-4xy-y²