Question

Tìm x , biết

3^x +3^x-2 = 810 với x ≥ 2 

Answer 1

\(3^x+3^{x-2}=810\)

<=> \(3^x+3^x:3^2=810\)

<=> \(3^x\left(1+\frac{1}{9}\right)=810\)

<=> \(3^x=729\)

<=>\(3^x=3^6\)

=> x=6

Answer 2

3^x +3^x-2 = 810 

\(\Rightarrow3^x\left(1+3^{-2}\right)=810\)

\(\Rightarrow3^x\left(1+\frac{1}{3^2}\right)=810\)

\(\Rightarrow3^x\left(1+\frac{1}{9}\right)=810\)

\(\Rightarrow3^x\cdot\frac{10}{9}=810\)

\(\Rightarrow3^x=729\)

\(\Rightarrow3^x=3^6\Leftrightarrow x=6\)

 

Answer 3

\(3^x+3^{x+2}=810\)

\(=>3^x+3^x:3^2=810\)

\(=>3^x.\left(1+\frac{1}{9}\right)=810\)

\(=>3^x.\frac{10}{9}=810\)

\(=>3^x=729\)

\(=>3^x=3^6\)

\(< =>x=6\)