(-x²+3xy-y²)-(-x²+4xy-y²)
=-x²+3xy-y²+x²-4xy+y²
=-xy
=-x²__+x²-xy-y²__________________+y²
(-x²+3xy-y²)-(-x²+4xy-y²)=-x²____________________+y²
(-x²+3xy-y²)-(-x²+4xy-y²)=-x²____________________+y²
数学人气:158 ℃时间:2020-02-02 20:57:40
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