\(\dfrac{3x+1}{2}=\dfrac{8}{3x+1}\)
\(\Rightarrow\left(3x+1.3x+1\right)=2.8\)
\(\Rightarrow\left(3x+1\right)^2=2.8\)
\(\Rightarrow\left(3x+1\right)^2=16\)
\(\Rightarrow\left(3x+1\right)^2=4^2\)
\(\Rightarrow3x+1=\pm4\)
\(\Rightarrow\left[{}\begin{matrix}3x+1=4\\3x+1=-4\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}3x=4-1\\3x=-4-1\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}3x=3\\3x=-5\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=3:3\\x=-5:3\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{-5}{3}\end{matrix}\right.\)
Vậy \(x=1;x=\dfrac{-5}{3}\)
(3x + 1)(3x + 1) = 8.2
(3x + 1)² = 16
3x + 1 = 4 hoặc 3x + 1 = -4
*) 3x + 1 = 4
3x = 3
x = 1
*) 3x + 1 = -4
3x = -4 - 1
3x = -5
x = -5/3
Vậy x = -5/3; x = 1
