How do you solve the quadratic equation by completing the square: ##x^2-12x+20=0##?

I found: ##x_1=10## ##x_2=2##

Rearrange your equation: ##x^2-12x=-20## add and subtract ##36##; ##x^2-12xcolor(red)(+36-36)=-20## ##x^2-12x+36=-20+36## so you can write: ##color(blue)((x-6)^2=16)## square root both sides: ##x-6=+-sqrt(16)=+-4## so you end up with two solutions: ##x_1=6+4=10## ##x_2=6-4=2##