how do you complete the square?

Question

I have the problem of x(squared)+2x=9. I understand completing the square to a degree, but I don't know how it works with a 2 in the x spot.

Answer 1

x^2+2x=9

take half of the coefficient of 2x and square it

(1/2)(2)=1 and 1^2=1

add 1 to both sides of the equation

x^2+2x+1=9+1

x^2+2x+1=10

(x+1)^2=10

take the square root of both sides

(x+1)=±√10

x=-1±√10

x=-1+√10

x=-1-√10