Question

Nick wrote the function p(x) = 17 + 42x – 7x2 in vertex form. His work is below.

p(x) = –7x2 + 42x + 17
p(x) = –7(x2 – 6x) + 17
(StartFraction negative 6 Over 2 EndFraction) squared = 9; p(x) = –7(x2 – 6x + 9) + 17
p(x) = –7(x – 3)2 + 17
When Nick checked his work it did not match the standard form function. Analyze Nick’s work. What was his mistake?

In step 1, he did not put the function in standard form correctly.
In step 2, he should have also factored –7 from the constant term, 17.
In step 3, he did not subtract –7(9) to keep the function equivalent.
In step 4, he did not write the perfect square trinomial correctly as a binomial squared.

Answer 1

step 3

Explanation:

he should have subtracted 9 to the outside.

whatever you do to the inside you must do to the opposite to the outside

so your final form must be -7(x-3)^2 + 8