# Quadratic formula proof review

CCSS Math: HSA.REI.B.4, HSA.REI.B.4a, HSA.REI.B.4b

A text-based proof (not video) of the quadratic formula.

The quadratic formula says that

for any quadratic equation like:

If you've never seen this formula proven before, you might like to watch a video proof, but if you're just reviewing or prefer a text-based proof, here it is:

## The proof

We'll start with the general form of the equation and do a whole bunch of algebra to solve for $x$. At the heart of the proof is the technique called $\blueD{\text{completing the square}}$. If you're unfamiliar with this technique, you may want to brush up by watching a video.

### Part 1: Completing the square

## Part 2: Algebra! Algebra! Algebra!

Remember, our goal is to solve for $x$.

And we're done!