\(x^2-3x-7=0\)
\(\Rightarrow x^2-3x+\dfrac{9}{4}-\dfrac{37}{4}=0\)
\(\Rightarrow\left(x-\dfrac{3}{2}\right)^2-\dfrac{37}{4}=0\)
\(\Rightarrow\left(x-\dfrac{3}{2}+\sqrt{\dfrac{37}{4}}\right)\left(x-\dfrac{3}{2}-\sqrt{\dfrac{37}{4}}\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}-\sqrt{\dfrac{37}{4}}\\x=\dfrac{3}{2}+\sqrt{\dfrac{37}{4}}\end{matrix}\right.\)