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Which of the following shows the correct first step to solve x^2 - 16x = -21 by completing the square?

A)x^2 - 16x + 64 = -21

B) x^2 - 16x + 64 = -21 + 64

C) x^2 - 16x + 16 = -21 + 16

D) x^2 - 16x + 8 = -21 + 8

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Answer:

I believe the answer would be B) x^2 - 16x + 64 = -21 + 64

Step-by-step explanation:

When you're completing the square you take the "middle" term (in this case it's -16) and you divide it by two, then square it. By doing that for this problem you get 64 (16/2 = 8 - 8^2 = 64; signs don't matter in this case because you multiply 2 negatives). You have to add that 64 to BOTH sides so that the equation evens out.

Ultimately, with it factored, the answer will be (x-8)^2