Question

已知2x+y=0,求x-2y/x²+xy乘(x²-y²)÷x²-4xy+4y

Answer 1

2x+y=0可得： y=-2x

于是

(x-2y)/(x²+xy) *( x²-y²) ÷(x²-4xy+4y²)/x

=(x-2y）/x(x+) *（ x+y)(x-y) ÷（x-2y)²/x

=(x-2y)/x(x+y) *( x+y)(x-y)x /(x-2y)²

=(x-y)/(x-2y)

把y=-2x代入(x-y)/(x-2y)有

(x+2x)/(x+4x)

=3x/(5x)

=3/5

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