The initial expression is:
[tex]x^2-16=6x[/tex]Now we can made it equal to 0 so:
[tex]x^2-6x-16=0[/tex]Now we can add 3^2 in bout side of the equations so:
[tex]\begin{gathered} x^2-6x-16+3^2=3^2 \\ (x-3)^2=16+9 \\ (x-3)^2=25 \end{gathered}[/tex]and we solve the perfect square so:
[tex]\begin{gathered} x-3=\sqrt[]{25} \\ x=5+3 \\ x=8 \end{gathered}[/tex]
