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$解:(1)由题意,$
$得2^{3}=2^{3b-2},3^{2b}=3^{a-3},$
$则\begin{cases}{ 3=3b-3, }\ \\ { 2b=a-3, } \end{cases}$
$解得a=7,b=2.$
$(2)m^{a+b}÷m^{a-b}=m^{2b}=m^{4}.$
$解:(2)∵3×9ⁿ×81ⁿ=3²⁵,$
$ ∴3×(3²)ⁿ×(3⁴)ⁿ=3²⁵.$
$ ∴3×3²ⁿ×3⁴ⁿ=3²⁵.$
$∴3^{1+2n+4n}=3²⁵.$
$ ∴1+2n+4n=25.$
$∴n=4.$
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C
A
$解:①8²⁰²²×(-0.125)²⁰²²\ $
$=8²⁰²²×0.125²⁰²²$
$=(8×0.125)²⁰²²\ $
$=1²⁰²²$
$=1.\ $
$②(\frac{12}{5})¹¹×(\frac{5}{6})¹³×(\frac{1}{2})¹²$
$=(\frac{12}{5})¹¹×(\frac{5}{6})¹¹×(\frac{5}{6})²×(\frac{1}{2})¹¹×\frac{1}{2}\ $
$=(\frac{12}{5}×\frac{5}{6}×\frac{1}{2})¹¹×\frac{25}{36}×\frac{1}{2}\ $
$=1¹¹×\frac{25}{72}$
$=1×\frac{25}{72}$
$=\frac{25}{72}.$