\(a,\Leftrightarrow\left(x-4\right)\left(x+4\right)=0\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\\ b,\Leftrightarrow5x^2+5x-12x-12=0\\ \Leftrightarrow\left(x+1\right)\left(5x-12\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=-1\\x=\dfrac{12}{5}\end{matrix}\right.\)