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: 13

Answer

Vertex: $(2,-2)$ Vertical intercept: $(0,4)$ Horizontal intercepts: $(3.15,0),(0.85,0)$

Work Step by Step

Given $$ f(x)=1.5 x^2-6 x+4. $$ The parabola is in its standard form, $f(x) = ax^2+bx+c$. The values of the constants are: $$ \begin{aligned} a&=1.5 \\ b&=-6 \\ c&=4. \end{aligned} $$ Find the $x$ and $y$ values of the vertex. $$ \begin{aligned} x & =\frac{-b}{2 a} \\ & =\frac{-(-6)}{2(1.5)} \\ & =2 \end{aligned} $$ $$ \begin{aligned} y & =1.5 \cdot 2^2-6 \cdot 2+4 \\ & =-2 \end{aligned} $$ $$ \text { Vertex: }(2,-2) $$ Find the vertical intercept. $$ \begin{aligned} &y=c=4\\ &\text { Vertical intercept: }(0,4) \end{aligned} $$ Find the horizontal intercept by setting $y= 0$ to find the $x$ values. $$ \begin{aligned} \frac{1.5 x^2-6 x+4}{1.5} & =\frac{0}{1.5} \\ x^2-4 x+\frac{40}{15} & =0 \\ x^2-4 x+2^2 & =\frac{-40}{15}+2^2 \\ (x-2)^2 & =\frac{4\cdot15-40}{15} \\ (x-2)^2 & =\frac{20}{15}\\ (x-2)^2&=\frac{20}{15}\\ (x-2)^2 & = \pm \sqrt{\frac{20}{15}} \\ x & =2 \pm \sqrt{\frac{20}{15}}\\ \end{aligned} $$ $$ \begin{aligned} x & =2+\sqrt{\frac{20}{15}} & x & =2-\sqrt{\frac{20}{15}} \\ & \approx3.15 & & \approx0.85 \end{aligned} $$ $$ \text {Vertical intercept:s }(3.15,0),(0.85,0) $$
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