（-x²+3xy-y²)-(-x²+4xy-y²)

（-x²+3xy-y²)-(-x²+4xy-y²)=-x²______

2个回答

（-x²+3xy-y²)-(-x²+4xy-y²)
=-x²+3xy-y²+x²-4xy+y²
=-xy
=-x²__+x²-xy-y²__________________+y²