How to complete the square? for this problem: x^2-6x+9=100 can you show me the steps i want to fully understand it : )

x^2 -6x +9 = 100
To complete the square:
1) Move any "non-x" terms to the right
x^2 -6x  = 91

2) Divide the equation by the coefficient of x^2 which in this case is "1" so the equation remains the same.
x^2 -6x  = 91

3) Take the coefficient of "x"
divide it by 2
then square it
add it to both sides of the equation
-6 divided by 2 = -3
-3 squared = 9
adding 9 to both sides of the equation

x^2 -6x  +9 = 100

4) Now take the square root of both sides of the equation:
x -3 = 10
x = 13
Let's not forget that the square root of 100 also equals -10
x -3 = -10
x = -7

Source:
http://www.1728.org/quadr2.htm