化简求值(x+5y)(x+4y)-(x-y)(x+y),其中x=一又2/5,y=-1/7

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化简求值(x+5y)(x+4y)-(x-y)(x+y),其中x=一又2/5,y=-1/7

化简求值(x+5y)(x+4y)-(x-y)(x+y),其中x=一又2/5,y=-1/7
化简求值(x+5y)(x+4y)-(x-y)(x+y),其中x=一又2/5,y=-1/7

化简求值(x+5y)(x+4y)-(x-y)(x+y),其中x=一又2/5,y=-1/7
=x^2+9xy+20y^2-(x^2-2xy+y^2)
=x^2+9xy+20y^2-x^2+2xy-y^2
=11xy+19y^2
=11*7/5*(-1/7)+19*(-1/7)^2
=-11/5+19/49
=-444/245

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