Big Ideas Math - Algebra 1, A Common Core Curriculum

Published by Big Ideas Learning LLC
ISBN 10: 978-1-60840-838-2
ISBN 13: 978-1-60840-838-2

Chapter 9 - Solving Quadratic Equations - 9.4 - Solving Quadratic Equations by Completing the Square - Exercises - Page 512: 39

Answer

The correct graph is $B$.

Work Step by Step

The given function is $\Rightarrow y=-x^2-4x-2$ Subtract $2$ from each side. $\Rightarrow y-2=-x^2-4x-2-2$ Simplify. $\Rightarrow y-2=-x^2-4x-4$ Factor out $-1$. $\Rightarrow y-2=-1(x^2+4x+4)$ Write the right side as the square of a binomial. $\Rightarrow y-2=-1(x+2)^2$ Write in vertex form. $\Rightarrow y=-1(x+2)^2+2$ The vertex is $(-2,2)$. Because $a$ is negative $(a=-1)$, the parabola opens down. Hence, the correct graph is $B$.
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