Đáp án+Giải thích các bước giải:
`(x+1/5)^2=9/25`
`\to(x+1/5)^2=(3/5)^2`
`\to` \(\left[ \begin{array}{l}x+\dfrac{1}{5}=\dfrac{3}{5}\\x+\dfrac{1}{5}=-\dfrac{3}{5}\end{array} \right.\)
`\to` \(\left[ \begin{array}{l}x=\dfrac{2}{5}\\x=-\dfrac{4}{5}\end{array} \right.\)
Vậy `x\in{-4/5;2/5}`