ĐK: \(\left\{{}\begin{matrix}x+7\ge0\\5x+2\ge0\end{matrix}\right.\Leftrightarrow x\ge-\frac{2}{5}\)
\(2\sqrt{x+7}=5x+2\)
\(\Leftrightarrow4\left(x+7\right)=\left(5x+2\right)^2\)
\(\Leftrightarrow25x^2+20x+4-4x-28=0\)
\(\Leftrightarrow25x^2+16x-24=0\)
\(\Delta'=8^2-25\cdot\left(-24\right)=664\)
phương trình có 2 nghiệm phân biệt:
\(\left\{{}\begin{matrix}x_1=\frac{-16+\sqrt{664}}{25}\left(tm\right)\\x_2=\frac{-16-\sqrt{664}}{25}\left(ktm\right)\end{matrix}\right.\)