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第61頁

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C

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

?$ =1$?

?$=\frac {b(a+b)-ab}{(a+b)(a-b)}$?

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

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

?$ =\frac {a^2}{a-2}$?

解：?$(1)n ·\frac n{n+1}=n-\frac {n}{n+1}$?

?$ (2)$?右邊?$=\frac {n(n+1)-n}{n+1}=\frac {n^2+n-n}{n+1}=\frac {n^2}{n+1}=n ·\frac n{n+1}=$?左邊

∴等式正確

A

$\frac {5}{3}$

2

-1

?$ =\frac {2x-3}{x^3}$?

?$=\frac {a^2-b^2}{(a-b)^2}$?

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

?$=\frac {2(x+3)+(1-x)(x-3)-6×2}{2(x+3)(x-3)}$?

?$ =\frac {2x+6+x-3-x^2+3x-12}{2(x+3)(x-3)}$?

?$ =\frac {-x^2+6x-9}{2(x+3)(x-3)}$?

?$ =-\frac {x-3}{2x+6}$?

?$=\frac {1-x+1+x}{1-x^2}+\frac 2{1+x^2}+\frac 4{1+x^4}$?

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

?$ =\frac {4(1+x^4)+4(1-x^4)}{1-x^8}$?

?$ =\frac 8{1-x^8}$?

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