a/ \(4^x+4^{x+1}=80\)
\(\Leftrightarrow4^x\left(1+4\right)=80\)
\(\Leftrightarrow4^x.5=80\)
\(\Leftrightarrow4^x=16\)
\(\Leftrightarrow4^x=4^2\)
\(\Leftrightarrow x=2\left(tm\right)\)
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b/ \(2^x+7\le39\)
\(\Leftrightarrow2^x\le32\)
\(\Leftrightarrow2^x\le2^5\)
\(\Leftrightarrow x\le5\)
\(\Leftrightarrow x\in\left\{0;1;2;3;4;5\right\}\)
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