Question

Giúp mình nha đang gấp lắm!!!

Tìm x,biết: 3^x+1+3^x+2+3^x+3-4.3^x=315

Answer 1

\(3^{x+1}+3^{x+2}+3^{x+3}-4.3^x=315\)

\(\Leftrightarrow3^x.3+3^x.3^2+3^x.3^3-4.3^x=315\)

\(\Leftrightarrow3^x.3+3^x.9+3^x.27-4.3^x=315\)

\(\Leftrightarrow3^x.\left(3+9+27-4\right)=315\)

\(\Leftrightarrow3^x.35=315\)\(\Leftrightarrow3^x=9\)

\(\Leftrightarrow3^x=3^2\)\(\Leftrightarrow x=2\)

Vậy \(x=2\)

Answer 2

            Bài làm :

Ta có :

\(3^{x+1}+3^{x+2}+3^{x+3}-4.3^x=315\)

\(\Leftrightarrow3^x.3+3^x.3^2+3^x.3^3-4.3^x=315\)

\(\Leftrightarrow3^x.3+3^x.9+3^x.27-4.3^x=315\)

\(\Leftrightarrow3^x.\left(3+9+27-4\right)=315\)

\(\Leftrightarrow3^x.35=315\)

\(\Leftrightarrow3^x=9\)

\(\Leftrightarrow3^x=3^2\)

\(\Leftrightarrow x=2\)

Vậy x=2