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[latex]27^x=81 \\ 3^{3x}=3^4 \\ 3x=4 \\ x= \frac{4}{3} \\ OTBET: \frac{4}{3} [/latex] [latex] \sqrt[4]{8^x} =16 \\ 8^{ \frac{x}{4} }=8^2 \\ \frac{x}{4} =2 \\ x=8 \\ OTBET:8[/latex] [latex]3^{x+1}+2*3^{x-1}=5 \\ 3*3^x+2* \frac{1}{3}*3^x =5 \\ t=3^x \\ 3t+ \frac{2}{3}t=5 \\ 9t+2t=15 \\ 11t=15 \\ t= \frac{15}{11} \\ 3^x= \frac{15}{11} \\ x=log_3 ( \frac{15}{11}) \\ OTBET: log_3 ( \frac{15}{11} ) [/latex] [latex]25^x-8*5^x-9=0[/latex] [latex]5^x=t \\ t^2-8t-9=0 \\ \left \{ {{t=9} \atop {t=-1}} \right. \\ \left \{ {{5^x=9} \atop {5^x \neq -1}} \right. \\ x=log_59 \\ OTBET: log_59[/latex]