we have the equation
[tex]x^2+12x-85=0[/tex]
step 1
Group similar terms and move the constant term to the right
[tex](x^2+12x)=85[/tex]
step 2
Complete the square
[tex]\begin{gathered} (x^2+12x+6^2-6^2)=85 \\ (x^2+12x+6^2)=85+6^2 \\ (x^2+12x+6^2)=121 \end{gathered}[/tex]
step 3
Rewrite as perfect squares
[tex](x+6)^2=121[/tex]
