\(25x^2-16=0\\ \Leftrightarrow25x^2=16\\ \Leftrightarrow\left[{}\begin{matrix}5x=4\\5x=-1\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{4}{5}\\x=-\dfrac{1}{2}\end{matrix}\right.\)
`25x^2 - 16 = 0`
`=> 25x^2 = 0 + 16`
`=> 25x^2 = 16`
`=> x^2 = 16 : 25`
`=> x^2 = 16/25`
`=>`\(\left[{}\begin{matrix}x^2=\left(\dfrac{4}{5}\right)^2\\x^2=\left(-\dfrac{4}{5}\right)^2\end{matrix}\right.\)
`=>`\(\left[{}\begin{matrix}x=\dfrac{4}{5}\\x=-\dfrac{4}{5}\end{matrix}\right.\)
`=> 25(x^2 - 16/25) = 0`
`=> x^2 = 16/25`
`=> x^2 = +-(4/5)^2`
`=> x = +-4/5`.
