Advanced Math practice question

Answer: 8

Factor: x² − 2x − 15 = (x − 5)(x + 3), so the x-intercepts are at x = 5 and x = −3. The distance between them is 5 − (−3) = 8.

Common wrong answers

If you answered 2

2 is the SUM of the intercepts (5 + (−3)), which is also the x-coordinate of the vertex times 2. The distance is the difference, 8.

If you answered 5

5 is one x-intercept, not the distance between the two. The other is at −3.

If you answered 15

15 is the product of the intercepts (with sign: 5 × −3 = −15), not their separation.

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