Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 4 Quadratic Functions and Factoring - 4.7 Complete the Square - 4.7 Exercises - Skill Practice - Page 289: 42


The vertex form of the function is $y=(x-2)^{2}+(-5).$ The vertex is $(2,-5)$.

Work Step by Step

$ y=x^{2}-4x-1\qquad$ ...prepare to complete the square. $ y+?=x^{2}-4x+?-1\qquad$ ...square half the coefficient of $x$. $(\displaystyle \frac{-4}{2})^{2}=(-2)^{2}=4\qquad$ ...complete the square by adding $4$ to each side of the expression $ y+4=x^{2}-4x+4-1\qquad$ ... write $x^{2}-4x+4$ as a binomial squared. $ y+4=(x-2)^{2}-1\qquad$ ...add $-4$ to each side of the expression $ y+4-4=(x-2)^{2}-1-4\qquad$ ...simplify. $ y=(x-2)^{2}-5\qquad$ ...write in vertex form $y=a(x-h)^{2}+k$. $y=(x-2)^{2}+(-5)$ The vertex form of a quadratic function is $y=a(x-h)^{2}+k$ where $(h,k)$ is the vertex of the function's graph. Here, $h=2,\ k=-5$, so the vertex is $(2,-5)$
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