Question

x的平方-y的平方分之y(x+y)-x(x+y)除以x的三次方+y的平方,其中x=2,y=-1

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Answer 1

[y(x-y)-x(x+y)]/(x²-y²)÷(x²+y²)/(x+y)
=(xy-y²-x²-xy)/[(x-y)(x+y)]*(x+y)/(x²+y²)
=-(x²+y²)/[(x-y)(x²+y²)]
=-1/(x-y)
=-1/(2+1)
=-1/3