解A-2B=(4x²-5xy+y²)-2(x²+3xy-5y²)=(4x²-2x²)+(-5xy-6xy)+(y²+10y²)=2x²-11xy+11y²-2A+3B=-2(4x²-5xy+y²)+3(x²+3xy-5y²)=(-8x²+3x
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