Question

3. (5^x -1) - 2 =70

Answer 1

\(3\left(5^x-1\right)-2=70\\ \Rightarrow3.5^x-3-2=70\\ \Rightarrow3.5^x-5=70\\ \Rightarrow3.5^x=75\\ \Rightarrow5^x=25\\ \Rightarrow x=2\)

Answer 2

\(3.\left(5^x-1\right)-2=70\)

\(\Leftrightarrow3.\left(5^x-1\right)=70+2\)

\(\Leftrightarrow3.\left(5^x-1\right)=72\)

\(\Leftrightarrow5^x-1=72:3\)

\(\Leftrightarrow5^x-1=24\)

\(\Leftrightarrow5^x=24+1\)

\(\Leftrightarrow5^x=25\)

\(\Leftrightarrow5^x=5^2\)

\(\Leftrightarrow x=2\)

Vậy \(x=2\)