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ta có: [tex]{log}_{54}168[/tex][tex]=\frac{{log}_{12}168}{{log}_{12}54}[/tex]
[tex]=\frac{{log}_{12}\left(24.7 \right)}{{log}_{12}24+{log}_{12}\frac{9}{4}}[/tex]
[tex]=\frac{{log}_{12}24+{log}_{12}7}{{log}_{12}24+2{log}_{12}12-6{log}_{12}2}[/tex]
[tex]=\frac{{log}_{12}24+{log}_{12}7}{{log}_{12}24+2-6{log}_{12}24+6{log}_{12}12}[/tex]
[tex]=\frac{b+\frac{1}{a}}{b+2-6b+6}[/tex]
[tex]=\frac{ab+1}{8a-5ab}[/tex]
 
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