What number must you add to complete the square? x^2+6x=15 A.6 B.12 C.9 D.3

C. 9

Step-by-step explanation:

To find the number we add to complete the square, we do (b/2)², or take b (which is 6), divide by 2 (which gives us 3), then square the result (which gives us 9):

6/2 = 3

3² = 9

9

Step-by-step explanation: To complete the square, we need a number to create a perfect square trinomial on the left side of the equation.

So the question is, what is that number?

Well it comes from a formula.

The number that we will need to complete the square will always

come from half the coefficient of the middle term squared.

In this case, that's half of 6 which is 3, squared, which is 9.

So we add 9 to both sides of the equation.

This will now allow the left side of the equation to factor.

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step-by-step explanation: