通分(x-y)÷(2x+2y)与xy÷(x+y)² 2mn÷4m²-9与(2m-3)(2m+3)
2个回答
2010-12-28
展开全部
2x+2y=2(x+y)
所以公分母2(x+y)²
所以(x-y)/(2x+2y)=(x-y)(x+y)/2(x+y)²=(x²-y²)/2(x+y)²
xy/(x+y)²=2xy/2(x+y)²
所以公分母2(x+y)²
所以(x-y)/(2x+2y)=(x-y)(x+y)/2(x+y)²=(x²-y²)/2(x+y)²
xy/(x+y)²=2xy/2(x+y)²
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