`#3107`
\(3^{8x+4}=81^{x+3}\\ \Rightarrow3^{8x+4}=\left(3^4\right)^{x+3}\\ \Rightarrow3^{8x+4}=3^{4x+12}\\ \Rightarrow8x+4=4x+12\\ \Rightarrow8x-4x=12-4\\ \Rightarrow4x=8\\ \Rightarrow x=8\div4\\ \Rightarrow x=2\\ \text{Vậy, x = 2.}\)
Lời giải:
$3^{8x+4}=81^{x+3}$
$3^{8x+4}=(3^4)^{x+3}$
$3^{8x+4}=3^{4(x+3)}$
$\Rightarrow 8x+4=4(x+3)$
$\Rightarrow 2x+1=x+3$
$\Rightarrow x=2$
\(3^{8x+4}=81^{x+3}\)
\(\Rightarrow\left(3^4\right)^{2x+1}=81^{x+3}\)
\(\Rightarrow81^{2x+1}=81^{x+3}\)
\(\Rightarrow2x+1=x+3\)
\(\Rightarrow2x-x=3-1\)
\(\Rightarrow x=2\)
