搜狗做题网2xy/x平方-y平方-x/x+y+y/y-x,其中x=3、y=2 先化简再求值
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2xy/x平方-y平方-x/x+y+y/y-x,其中x=3、y=2 先化简再求值
2xy/(x^2-y^2)-x/(x+y)+y/(y-x)
=2xy/(x^2-y^2)-x/(x+y)-y/(x-y)
=2xy/[(x-y)(x+y)]-x(x-y)/[(x-y)(x+y)]-y(x+y)/[(x-y)(x+y)]
=[2xy-x(x-y)-y(x+y)]/[(x-y)(x+y)]
=[2xy-x^2+xy-xy-y^2]/[(x-y)(x+y)]
=-[x^2+y^2-2xy]/[(x-y)(x+y)]
=-(x-y)^2/[(x-y)(x+y)]
=-(x-y)/(x+y)
=-(3-2)/(3+2)
=-1/5
=2xy/(x^2-y^2)-x/(x+y)-y/(x-y)
=2xy/[(x-y)(x+y)]-x(x-y)/[(x-y)(x+y)]-y(x+y)/[(x-y)(x+y)]
=[2xy-x(x-y)-y(x+y)]/[(x-y)(x+y)]
=[2xy-x^2+xy-xy-y^2]/[(x-y)(x+y)]
=-[x^2+y^2-2xy]/[(x-y)(x+y)]
=-(x-y)^2/[(x-y)(x+y)]
=-(x-y)/(x+y)
=-(3-2)/(3+2)
=-1/5
5xy平方-2x平方y+[3xy平方-(4xy-2x平方y-2x平方y)],其中x=-2,y=-1求值
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