The given equation is:
[tex]x^2-12x=28[/tex]Add (12/2)^2=36 on both sides of the equation.
[tex]\begin{gathered} x^2-12x+(\frac{12}{2})^2=28+(\frac{12}{2})^2 \\ x^2-12x+36^{}=28+36 \\ (x+6)^2=64 \end{gathered}[/tex]Therefore, adding 36 to both sides of the equation complete the square.
Hence, option C is correct.
