First subtract 100 from both sides to get x^2-20x=-100 then find c. (-b/2)^2 is the formula. then c=100 so add 100 to both sides. x^2-20x+100=200. Then Factor. (x-10)^2=0 is what you should get. then do square root. x-10=0. So now add 10 to both sides and you get x=10. Tada!
