Explain how the quadratic formula is connected to the completing the square process.

If you start with the equation:  ax² + bx + c  =  0

and complete the square on this equation, you will end with the quadratic formula.

Morgan Tud’s Magick of the Quadratic gives an animated formulaic and pictographic overview of the process. 

Source: Morgan Tud Magick of the Quadratic

GA