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第76頁

信息發(fā)布者：

$解：因?yàn)?\frac {1}{x}-\frac {1}{y}=3?$

$? \frac {1}{x}-\frac {1}{y}=\frac {y-x}{xy}=3?$

$ 所以?y-x=3xy?$

$ 原式?=\frac {x-(y-x)-y}{2x+y-x-2y}?$

$? =\frac {2(x-y)}{x-y}?$

$? =2?$

D

A

$解：原式?=\frac {a-b}{a-b}×\frac {ab}{a-b}?$

$? =\frac {ab}{a-b}?$

$解：原式?=\frac {x(x+2)-x(x-2)}{(x-2)(x+2)}×\frac {2-x}{4x}?$

$? =\frac {4x}{(x+2)(x-2)}×\frac {2-x}{4x}?$

$? =-\frac {1}{x+2}?$

$解：原式?=1-\frac {a-b}{a+2b}×\frac {(a+2b)2}{(a-b)(a+b)}?$

$? =1-\frac {a+2b}{a+b}?$

$? =-\frac {a+b}$

$解：原式?=\frac {a2-b2+2b2}{a-b}?$

$? =\frac {a2+b2}{a-b}?$

$解：原式?=\frac {(x-y)2+4xy}{x-y}×\frac {(x+y)2-4xy}{x+y}?$

$?=\frac {(x+y)2}{x-y}×\frac {(x-y)2}{x+y}?$

$?=(x+y)(x-y)?$

$? =x2-y2$

$解：原式?=\frac {m+2-(m-2)}{(m+2)(m-2)}??+\frac {2(m-1)-2(m+1)}{(m+1)(m-1)}?$

$? =\frac {4}{(m+2)(m-2)}-\frac {4}{(m+1)(m-1)}?$

$? =\frac {12}{(m+2)(m-2)(m+1)(m-1)}?$

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