a, \(x^2-x-30=0\)
\(\Leftrightarrow x^2-6x+5x-30=0\)
\(\Leftrightarrow x\left(x-6\right)+5\left(x-6\right)=0\)
\(\Leftrightarrow\left(x+5\right)\left(x-6\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+5=0\\x-6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=6\end{matrix}\right.\)
Vậy x = -5 hoặc x = 6