\(4x^2-36x+56=0\)
\(\Rightarrow4\left(x^2-9x+14\right)=0\)
\(\Rightarrow4\left(x^2-7x-2x+14\right)=0\)
\(\Rightarrow4x\left(x-2\right)-7\left(x-2\right)=0\)
\(\Rightarrow4\left(x-7\right)\left(x-2\right)=0\)
\(\Rightarrow\left(x-7\right)\left(x-2\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-7=0\\x-2=0\end{matrix}\right.\)
\(\Rightarrow x=7;x=2\).
\(4x^2-36x+56=0\)
\(\Leftrightarrow\left(2x\right)^2-2\cdot2x\cdot9+9^2-25=0\)
\(\Leftrightarrow\left(2x-9\right)^2-25=0\)
\(\Leftrightarrow\left(2x-9\right)^2=25\Leftrightarrow\left[{}\begin{matrix}2x-9=5\\2x-9=-5\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=7\\x=2\end{matrix}\right.\)
Vậy....................
