Jeff began deriving the quadratic formula. (rest of the question in photo)

For this case we have the following expression:
 ax2 + bx + c = 0
 Rewriting the expression we have:
 x2 + (b / a) x + (c / a) = 0
 Then, to solve the equation by completing squares, the next step is:
 x2 + (b / a) x + (c / a) - (c / a) = - (c / a)
 
 Subtract c / a from both sides

Ibelieve that c. recording would work best.