Intermediate Algebra: Connecting Concepts through Application

Published by Brooks Cole
ISBN 10: 0-53449-636-9
ISBN 13: 978-0-53449-636-4

Chapter 4 - Quadratic Functions - 4.7 Graphing Quadratics from Standard Form - 4.7 Exercises - Page 385: 11

Answer

Vertex: $(-1.2, 2.8)$ Vertical intercept: $(0,10)$ Horizontal intercepts: None

Work Step by Step

Given $$ g(x)=5 x^2+12 x+10. $$ The parabola is in its standard form, $f(x) = ax^2+bx+c$. The values of the constants are: $$ \begin{aligned} a&=5 \\ b&=12 \\ c&=10. \end{aligned} $$ Find the $x$ and $y$ values of the vertex. $$ \begin{aligned} x&=\frac{-b}{2a} \\ x&=\frac{-(12)}{2(5)} \\ x&=-1.2\\ y&= 5\cdot (-1.2)^2+12\cdot (-1.2)+10\\ &= 2.8. \end{aligned} $$ The vertex is $(-1.2,2.8)$. The horizontal intercept is found by setting the $y$ component of the parabola to zero and solving for $x$. $$ \begin{aligned} 5x^2+12x+10&=0. \end{aligned} $$ $$ \begin{aligned} & x=\frac{-12 \pm \sqrt{12^2-4 \cdot 5 \cdot 10}}{2 \cdot 5} \\ & x=\frac{-12 \pm \sqrt{-56}}{10}. \end{aligned} $$ There is no horizontal intercept since we cannot take the square root of a negative number. The graph has a vertical intercept for $x= 0$ and $y = c = 10$. The vertical intercept is $(0,10)$.
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