\(\left(x+0,8\right)^2=0,25\\ \Leftrightarrow\left[{}\begin{matrix}\left(x+0,8\right)^2=\left(0,5\right)^2\\\left(x+0,8\right)^2=\left(-0,5\right)^2\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x+0,8=0,5\\x+0,8=-0,5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0,5-0,8=-0,3\\x=-0,5-0,8=-1,3\end{matrix}\right.\)