设A=x²-xy,B=xy+y²,求:(1):A+B(2):3A-B
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设A=x²-xy,B=xy+y²,求:(1):A+B(2):3A-B
设A=x²-xy,B=xy+y²,求:(1):A+B(2):3A-B
设A=x²-xy,B=xy+y²,求:(1):A+B(2):3A-B
A+B
=(x²-xy)+(xy+y²)
=x²-xy+xy+y²
=x²+y²
3A-B
=3(x²-xy)-(xy+y²)
=3x²-3xy-xy-y²
=3x²-4xy-y²