化简求值:2(x+y)²-5(x+y)(x-y)+3(x-y)²,其中x=2分之5,y=5分之3
问题描述:
化简求值:2(x+y)²-5(x+y)(x-y)+3(x-y)²,其中x=2分之5,y=5分之3
答
原式=2x²+4xy+2y²-5x²+5y²+3x²-6xy+3y²
=-2xy+10y²
=-2*5/2*3/5+10*9/25
=-3+18/5
=-3/5