Advanced Math practice question

Answer: 4

The minimum of x² − 4x + c is at x = −(−4)/(2·1) = 2, where h(2) = 4 − 8 + c = c − 4. Setting c − 4 = 0 gives c = 4. (Then h(x) = (x − 2)², which is never negative and equals 0 at x = 2.)

Common wrong answers

If you answered 2

2 is the x-coordinate of the minimum, not c.

If you answered 16

16 is (−4)², which appears in the discriminant but is not c.

If you answered -4

−4 comes from setting c − 4 = −8, or from a sign slip in h(2).

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