Question

X^2 - 10x - 20 = 0, which number would have to be added to "complete the square"?

Answer 1

25 to both sides

Explanation:

Group x² and x terms

(x² - 10x ) - 20

complete the square

(x² - 10x +25 ) -20 -25

(x-5)² -45

Answer 2

45

Explanation:

When you're completing the square you're adding (b/2)^2 which in this case is (-5)^2 or 25. This is because when you rewrite it as a square binomial you write it in the form (x+(b/2))^2 which is going to result in x^2+b+(b/2)^2. Since you need to reach 25 you need to add 45 since the last value is at -20.