a)
`-4+x^2=0`
`->x^2=4`
`->x=±2`
b)
`(2x-3)^2=9x^2`
`->(2x-3)^2-(3x)^2=0`
`->(2x-3-3x)(2x-3+3x)=0`
`->(-x-3)(5x-3)=0`
`->`\(\left[ \begin{array}{l}-x-3=0\\5x-3=0\end{array} \right.\)
`->`\(\left[ \begin{array}{l}x=-3\\x=\dfrac{3}{5}\end{array} \right.\)
c)
`x^2-x-12=0`
`->x^2-2.x. 1/2+1/4-49/4=0`
`->(x-1/2)^2=49/4`
`->`\(\left[ \begin{array}{l}x-\dfrac{1}{2}=\dfrac{7}{2}\\x-\dfrac{1}{2}=\dfrac{-7}{2}\end{array} \right.\)
`->`\(\left[ \begin{array}{l}x=4\\x=-3\end{array} \right.\)
d)
`2x^2-x-6=0`
`->2x^2+2x-3x-6=0`
`->2x(x+2)-3(x+2)=0`
`->(2x-3)(x+2)=0`
`->`\(\left[ \begin{array}{l}2x-3=0\\x+2=0\end{array} \right.\)
`->`\(\left[ \begin{array}{l}x=\dfrac{3}{3}\\x=-2\end{array} \right.\)
