Question

Tìm \(x\) biết \(7^{x+2}+2.7^{x-1}=345\)

 

Answer 1

\(7^{x-1+3}+2.7^{x-1}=345\Leftrightarrow7^{x-1}\left(7^3+2.1\right)=345\)

\(\Leftrightarrow7^{x-1}.345=345\Leftrightarrow7^{x-1}=1\Leftrightarrow7^{x-1}=7^0\Leftrightarrow x-1=0\Rightarrow x=1\)

Vậy x= 1

Answer 2

=> \(7^{x-1}.7^3+2.7^{x-1}=345\)

=> \(7^{x-1}.\left(7^3+2\right)=345\)

=> \(7^{x-1}.345=345\Rightarrow7^{x-1}=1\Rightarrow x-1=0\) => x = 1 

Answer 3

\(7^{x+2}+2.7^{x-1}=345\)

\(7^{x-1+3}+2.7^{x-1}=345\)

\(7^{x-1}.7^3+2.7^{x-1}=345\)

\(7^{x-1}\left(7^3+2\right)=345\)

\(7^{x-1}\left(343+2\right)=345\)

\(7^{x-1}.345=345\)

\(7^{x-1}=345:345\)

\(7^{x-1}=1\)

\(7^{x-1}=7^0\Rightarrow x-1=0\)

=>\(x=1\)

Vậy x=1

Answer 4

\(7^x.7^2+2.7^x:14=345\)

\(7^x.49+2.7^x:14=345\)

Từ đây bạn bấm máy tính là ra