## Algebra 1

Published by Prentice Hall

# Chapter 9 - Quadratic Functions and Equations - 9-2 Quadratic Functions - Practice and Problem-Solving Exercises: 23

#### Answer

Axis of symmetry: x= -2.5 Vertex: (-2.5, 12.5) The graph is shown below:

#### Work Step by Step

$y = -2x^{2} - 10x$ The standard form for a quadratic equation is $y = ax^{2} + bx + c$ So a= -2, b= -10, and c= 0 Axis of symmetry: The formula for axis of symmetry is $x= \frac{-b}{2a}$ $x= \frac{-(-10)}{2(-2)}$ $x= \frac{10}{-4}$ x= -2.5 Vertex: Plug in the x value of the axis of symmetry to find the y value of the vertex. $y = -2x^{2} - 10x$ $y = -2(-2.5)^{2} - 10(-2.5)$ y= 12.5 The vertex is (-2.5, 12.5) We plot the vertex on the graph. Since the a value is -2 and is negative the parabola opens downwards. So we graph a parabola starting from the vertex and then graphing it downwards.

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