\(7^{x-1+3}+2.7^{x-1}=345\Leftrightarrow7^{x-1}\left(7^3+2.1\right)=345\)
\(\Leftrightarrow7^{x-1}.345=345\Leftrightarrow7^{x-1}=1\Leftrightarrow7^{x-1}=7^0\Leftrightarrow x-1=0\Rightarrow x=1\)
Vậy x= 1
=> \(7^{x-1}.7^3+2.7^{x-1}=345\)
=> \(7^{x-1}.\left(7^3+2\right)=345\)
=> \(7^{x-1}.345=345\Rightarrow7^{x-1}=1\Rightarrow x-1=0\) => x = 1
\(7^{x+2}+2.7^{x-1}=345\)
\(7^{x-1+3}+2.7^{x-1}=345\)
\(7^{x-1}.7^3+2.7^{x-1}=345\)
\(7^{x-1}\left(7^3+2\right)=345\)
\(7^{x-1}\left(343+2\right)=345\)
\(7^{x-1}.345=345\)
\(7^{x-1}=345:345\)
\(7^{x-1}=1\)
\(7^{x-1}=7^0\Rightarrow x-1=0\)
=>\(x=1\)
Vậy x=1
\(7^x.7^2+2.7^x:14=345\)
\(7^x.49+2.7^x:14=345\)
Từ đây bạn bấm máy tính là ra
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