Ta có : 2n + 1 - 7 = 121
=> 2n + 1 = 128
=> 2n + 1 = 27
=> n + 1 = 7
=> n = 6
a) Ta có: \(2^{n+1}-7=121\)
\(\Rightarrow2^{n+1}=128\)
\(\Rightarrow2^{n+1}=2^7\)
\(\Rightarrow n+1=7\Rightarrow n=6\)
b) Ta có: \(10.6^{n-2}=2160\)
\(\Rightarrow6^{n-2}=216\)
\(\Rightarrow6^{n-2}=6^3\)
\(\Rightarrow n-2=3\Rightarrow n=5\)
c) Ta có:\(2.3^{n+1}+5.3^{n+1}=\)63
\(\Rightarrow3^{n+1}.\left(2+5\right)=63\)
\(\Rightarrow3^{n+1}.7=63\)
\(\Rightarrow3^{n+1}=9\)
\(\Rightarrow3^{n+1}=3^2\)
\(\Rightarrow n+1=2\Rightarrow n=1\)
d) n\(\in\)\(\left\{0;1;2;3;4\right\}\)
e)Ta có: \(6.4^{2n-1}=384\)
\(\Rightarrow4^{2n-1}=64\)
\(\Rightarrow4^{2n-1}=4^3\)
\(\Rightarrow2n-1=3\)
\(\Rightarrow2n=4\Rightarrow n=2\)
