Question

The first three steps for completing the square to solve a quadratic equation are shown. What number goes in the boxes to complete the third step?

Answer 1

16

Explanation:

The x-coefficient is -8. Half of -8 is -4. The number that goes in the boxes is the square of -4: (-4)² = 16.

Answer 2

9514 1404 393

Answer:

C. 16

Explanation:

The x-coefficient is -8. Half that is -4. The number that goes in the boxes is the square of -4: (-4)² = 16.

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It can help to keep in mind what the square of a binomial looks like:

(x -a)² = x² -2ax +a²

The coefficient of x is -2a. The constant is the square of half that (-2a/2)² = a².