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

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

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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