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 - 4.6 Solving Quadratic Equations by Using the Quadratic Formula - 4.6 Exercises - Page 373: 50

Answer

$x = -2.48, x= 2.15$

Work Step by Step

Use either the square root method, the quadratic formula or factoring. $$ \begin{aligned} \frac{3}{4} x^2+\frac{1}{2} x-7 & =\frac{1}{4} x-3 \\ \frac{3}{4} x^2+\frac{1}{2} x & =\frac{1}{4} x-3+7 \\ \left(\frac{3}{4} x^2+\frac{1}{2} x\right) \cdot 4 & =\left(\frac{1}{4} x+4\right) \cdot 4 \\ 3 x^2+2 x & =x+16 \\ 3 x^2+2 x-x & =16 \\ 3 x^2+x & =16. \end{aligned} $$ Bring the equation to the standard form and solve it. $$ \begin{aligned} & 3 x^2+x-16=0 \\ & \begin{aligned} x & =\frac{-1 \pm \sqrt{1^2+4(16)(3)}}{2(3)} \\ & =\frac{-1 \pm \sqrt{193}}{6} \\ & \approx0.1667 \pm 2.315. \end{aligned} \end{aligned} $$ We have: $$ \begin{aligned} x & =-0.1667-2.315 \\ & =-2.48 \end{aligned}$$ $$\begin{aligned} x & =-0.1167+2.315 \\ & =2.15 \end{aligned}$$ Define the following version of the function and plot it. We see that the zeros are where they should be. $$ f(x)= \frac{3}{4} x^2+\frac{1}{4} x-4.$$
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