Answer:
C. Add 9 to both sides of the equation.
Step-by-step explanation:
Given
[tex]x^2 - 6x = 15[/tex]
Required
Complete the squares
We have:
[tex]x^2 - 6x = 15[/tex]
---------------------------------------------
Take the coefficient of -6 i.e. -3
Square it (-3)^2 = 9
Add 9 to both sides
---------------------------------------------
Hence, C is correct