Advanced Math practice question

Answer: 4

The axis of symmetry is x = −b/(2a) = −(−8)/(2·1) = 8/2 = 4, which is the vertex's x-coordinate. Equivalently, the roots are x = 2 and x = 6 (from factoring x² − 8x + 12), and their midpoint is 4. The trap is using −b/(2a) with the wrong sign and getting −4.

Common wrong answers

If you answered 2

That's one of the x-intercepts (from x² − 8x + 12 = (x−2)(x−6)). The vertex sits at the midpoint of the two roots 2 and 6, which is 4.

If you answered 6

That's the other x-intercept, not the vertex. Average the two roots, 2 and 6, to get x = 4.

If you answered -4

You applied −b/(2a) but dropped a sign: b is −8, so −b = +8, giving 8/2 = 4, not −4.

If you answered -8

That's b itself. You still need to compute −b/(2a) = 8/2 = 4.

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