Question

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

Answer 1

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)
Answer:
Subtract c / a from both sides