In this video I solve the quadratic equation by completing the square to obtain the famous quadratic formula. I had done a similar video 13 years ago so I thought it was time to do an updated one. Completing the square involves working backwards from the quadratic equation to obtain a form that has a square, that is of the form (x + d)2. From here we can take the square root and rearrange to solve for x, which obtains 2 values because of the nature of the square root.
Notes: Recap on the Quadratic Formula
Written notes — mirrored from Cubic Formula Proof, which walks through the complete derivation.
Recall my earlier video on the Quadratic Formula:
In that video I derived it by Completing the Square.
- Watch on: 3Speak · YouTube · Telegram
- Full written notes: Cubic Formula Proof
- Playlist: Cubic Formula Proof YouTube playlist
- More math: mes.fm/math
Originally posted on the Hive blockchain →
Text and image retrieved from the Hive blockchain on September 24, 2026.