\(a,x^2-3x-4=0\\ \Rightarrow\left(x^2-4x\right)+\left(x-4\right)=0\\ \Rightarrow x\left(x-4\right)+\left(x-4\right)=0\\ \Rightarrow\left(x-4\right)\left(x+1\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=4\\x=-1\end{matrix}\right.\\ b,x^2+5x-6=0\\ \Rightarrow\left(x^2+6x\right)-\left(x+6\right)=0\\ \Rightarrow x\left(x+6\right)-\left(x+6\right)=0\\ \Rightarrow\left(x+6\right)\left(x-1\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=-6\\x=1\end{matrix}\right.\)
\(c,x^2-x-6=0\\ \Rightarrow\left(x^2-3x\right)+\left(2x-6\right)=0\\ \Rightarrow x\left(x-3\right)+2\left(x-3\right)=0\\ \Rightarrow\left(x-3\right)\left(x+2\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=3\\x=-2\end{matrix}\right.\\ d,3x^2-5x+2=0\\ \Rightarrow\left(3x^2-3x\right)-\left(2x-2\right)=0\\ \Rightarrow3x\left(x-1\right)-2\left(x-1\right)=0\\ \Rightarrow\left(x-1\right)\left(3x-2\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{2}{3}\end{matrix}\right.\)
\(e,2x^2-7x+5=0\\ \Rightarrow\left(2x^2-2x\right)-\left(5x-5\right)=0\\ \Rightarrow2x\left(x-1\right)-5\left(x-1\right)=0\\ \Rightarrow\left(x-1\right)\left(2x-5\right)\\ \Rightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{5}{2}\end{matrix}\right.\)
