`(3x+1)^2=25.4`
<=> `(3x+1)^2=10^2`
<=> `3x+1=10` hoặc `3x+1=-10`
<=> `x=3` hoặc `x=-11/3`
\(\left(3x+1\right)^2=25.4\\ < =>\sqrt{\left(3x+1\right)^2}=\sqrt{100}< =>3x+1=10\\ < =>3x=9\\ < =>x=3\\\)
Ta có : (3x + 1)2 = 25 . 4
=> (3x + 1)2 = 100
=> (3x + 1) = 102
=> 3x + 1 = 10
=> x = 3