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第97页

信息发布者：

$ A$

$\frac{7}{2}$

$1012\frac{1}{2}$

解：$(\frac {y}{-3x})^3·\frac {x}{y^2}÷(-\frac {y}{x})^4$

$ =-\frac {y^3}{27x^3}·\frac {x}{y^2}·\frac {x^4}{y^4}$

$ =-\frac {x^2}{27y^3}$

解：$(\frac {8}{a+3}+a-3)÷\frac {a^2+2a+1}{a+3}$

$ =(\frac {8}{a+3}+\frac {(a-3)(a+3)}{a+3})·\frac {a+3}{(a+1)^2}$

$ =\frac {a^2-1}{a+3}·\frac {a+3}{(a+1)^2}$

$ =\frac {(a+1)(a-1)}{(a+1)^2}$

$ =\frac {a-1}{a+1}$

解：原式$=(1-\frac {1}{a+2})÷\frac {a^2-1}{a+2}$

$ =\frac {a+1}{a+2}·\frac {a+2}{(a+1)(a-1)}$

$ =\frac {1}{a-1}$

$ $当$a=3$时，原式$=\frac {1}{3-1}=\frac {1}{2}$

解：原式$=(\frac {a}{a-b}-\frac {a^2}{a^2-2ab+b^2})÷(\frac {a}{a+b}-\frac {a^2}{a^2-b^2})+1$

$ =\frac {a(a-b)-a^2}{(a-b)^2}÷\frac {a(a+b)-a^2}{(a+b)(a-b)}+1$

$ =\frac {-ab}{(a-b)^2}÷\frac {-ab}{(a+b)(a-b)}+1$

$ =\frac {-ab}{(a-b)^2}·\frac {(a+b)(a-b)}{-ab}+1$

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

$ =\frac {2a}{a-b}$

$ $当$a=\frac {2}{3}，b=-3$时，原式$=\frac {2×\frac {2}{3}}{\frac {2}{3}-(-3)}=\frac {4}{11}$

解：原式$=(a+1+\frac {1}{a-1})÷\frac {a^3-2a^2}{a^2-4a+4}$

$ =(\frac {a^2-1}{a-1}+\frac {1}{a-1})·\frac {(a-2)^2}{a^2(a-2)}$

$ =\frac {a^2}{a-1}·\frac {(a-2)^2}{a^2(a-2)}$

$ =\frac {a-2}{a-1}$

∵$a^2-4=0，a-2≠0$，∴$a=-2$，

$ $当$a=-2$时，原式$=\frac {-2-2}{-2-1}=\frac {4}{3}$