`a, 4x^2 -49=0`
`(2x+7)(2x-7)=0`
$⇒\left[ \begin{array}{l}2x+7=0\\2x-7=0\end{array} \right.⇒\left[ \begin{array}{l}2x=-7\\2x=7\end{array} \right.⇒\left[ \begin{array}{l}x=\dfrac{-7}{2}\\x=\dfrac{7}{2}\end{array} \right.$
`b, (x-4)^2 -36=0`
`(x-4)^2 =36`
`x-4=+-6`
$⇒\left[ \begin{array}{l}x-4=6\\x-4=-6\end{array} \right.⇒\left[ \begin{array}{l}x=10\\x=-2\end{array} \right.$
`c, x^2 -36=0`
`x^2 =36`
`x=+-6`
`d, 25x^2 -0,64=0`
`(5x-0,8)(5x+0,8)=0`
$⇒\left[ \begin{array}{l}5x-0,8=0\\5x+0,8=0\end{array} \right.⇒ \left[ \begin{array}{l}5x=0,8\\5x=-0,8\end{array} \right.⇒ \left[ \begin{array}{l}x=\dfrac{0,8}{5}\\x=\dfrac{-0,8}{5}\end{array} \right.⇒\left[ \begin{array}{l}x=\dfrac{8}{50}\\x=\dfrac{-8}{50}\end{array} \right.⇒\left[ \begin{array}{l}x=\dfrac{4}{25}\\x=\dfrac{-4}{25}\end{array} \right.$
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