Completing the square for circle equations - Khan Academy

https://www.khanacademy.org/math/algebra2/conics_precalc/circles-tutorial-precalc/v/completing-the-square-to-write-equation-in-standard-form-of-a-circle?_escaped_fragment_=

Another Example of Completing the square - with factoring out a coefficient first -

https://www.youtube.com/watch?v=3Ixp3PeAErI

Longer video...covers a few examples...including with coefficients

https://www.youtube.com/watch?v=rmy5hZJCcl0