Question

I just have a question, how did they get 36?.

Answer 1

see below

Explanation:

They are completing the square

x^2 +12x +29

Take the coefficient of the x term

12

Divide by 2

12/2 = 6

Square it

6^2 = 36

Add 36 and subtract 36

(x^2 +12x +36) -36 +29

Inside the parentheses becomes ( x+6)^2