Advanced Math practice question

Answer: 10

(x + 5)² = x² + 10x + 25. Subtracting x² + 25 leaves 10x, so k = 10.

Common wrong answers

If you answered 0

0 would mean (x + 5)² equals x² + 25, a common but false belief.

If you answered 5

5 forgets to double the cross term: 2 × 5 = 10.

If you answered 25

25 is the constant that cancels, not k.

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