\(4x^2-28=0\)
\(4x^2=28\)
\(x^2=7\)
\(\)
\(4x^2-28=0\)
\(\Leftrightarrow4\left(x^2-7\right)=0\)
\(\Leftrightarrow x^2-7=0\)
\(\Leftrightarrow x^2=7\)
\(\Leftrightarrow x=\pm\sqrt{7}\)
\(x^2+36=12x\)
\(\Rightarrow x^2+36-12x=0\)
\(\Rightarrow\left(x-6\right)^2=0\)
\(\Rightarrow x-6=0\)
\(\Rightarrow x=6\)
\(x^2+36=12x\)
\(\Leftrightarrow x^2-12x+36=0\)
\(\Leftrightarrow\left(x-6\right)^2=0\)
\(\Leftrightarrow x-6=0\Leftrightarrow x=6\)
