a) \(9< 3^x< 243\)
\(\Leftrightarrow3^2< 3^x< 3^5\)
\(\Rightarrow x\in\left\{3;4\right\}\)
b) Sửa đề: \(3^4.3^x\div9=27\)
\(\Leftrightarrow3^{x+4}=3\)
\(\Rightarrow x+4=1\)
\(\Rightarrow x=-3\)
c) \(3^x\div3^2=243\)
\(\Leftrightarrow3^{x-2}=3^5\)
\(\Rightarrow x-2=5\)
\(\Rightarrow x=7\)
d) \(25< 5^x< 3125\)
\(\Leftrightarrow5^2< 5^x< 5^5\)
\(\Rightarrow x\in\left\{3;4\right\}\)
e) \(2^x-64=2^6\)
\(\Leftrightarrow2^x=64+64=128\)
\(\Leftrightarrow2^x=2^7\)
\(\Rightarrow x=7\)
f) \(2^x\div16=128\)
\(\Leftrightarrow2^x=2^7.2^4\)
\(\Leftrightarrow2^x=2^{11}\)
\(\Rightarrow x=11\)
