If using the method of completing the square to solve the quadratic equation x^2-4x+10=0, which number would have to be added to "complete the square"?

4

Step-by-step explanation:

Given

x² - 4x + 10 = 0

subtract 10 from both sides

x² - 4x = - 10

To complete the square

add (half the coefficient of the x - term) ² to both sides

x² + 2 ( - 2) x + 4 = - 10 + 4

(x - 2) ² = - 6

To complete the square add 4