The first six steps of the derivation of the quadratic formula are listed below, find the 7th,8th, and 9th steps

The purpose of the quadratic formula is to easily obtain the x-coordinate of the vertex's location. The goal is to solve the equation by isolating x on one side of the equation, just like you would any other equation.

In step 7, take the square root of both sides. Note that you must account for the negative side of the square root, so add the +/- to the right side (not necessary for the left side because you want the x to be positive when you are finished, and you still get the same answer even if you assume the left side is negative).

Next, subtract b/2a from both sides and simplify the denominator of the root to be 2a.

Finally combine the terms to have a single denominator.