Question

8+2x(x-4)=20

Answer 1

\(\Rightarrow2\left(x-4\right)=12\\ \Rightarrow x-4=6\\ \Rightarrow x=10\)

Answer 2

\(\Leftrightarrow2x\left(x-4\right)=12\\ \Leftrightarrow x\left(x-4\right)=6\\ \Leftrightarrow x^2-4x-6=0\\ \Leftrightarrow\left(x^2-4x+4\right)-10=0\\ \Leftrightarrow\left(x-2\right)^2-10=0\\ \Leftrightarrow\left(x-2-\sqrt{10}\right)\left(x-2+\sqrt{10}\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=2+\sqrt{10}\\x=2-\sqrt{10}\end{matrix}\right.\)