Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

Published by Pearson
ISBN 10: 0-32184-874-8
ISBN 13: 978-0-32184-874-1

Chapter 11 - Quadratic Functions and Equations - 11.1 Quadratic Equations - 11.1 Exercise Set - Page 708: 98

Answer

5, 6 and 7

Work Step by Step

Assume that the three consecutive integers are $x,x+1$ and $x+2$. According to the question, ${{x}^{2}}+\left( x+1 \right)\left( x+2 \right)=67$ Simplify the quadratic equation $\begin{align} & {{x}^{2}}+\left( x+1 \right)\left( x+2 \right)=67 \\ & {{x}^{2}}+{{x}^{2}}+2x+x+2=67 \\ & 2{{x}^{2}}+3x=67-2 \\ & 2{{x}^{2}}+3x-65=0 \end{align}$ The solution of the quadratic equation $a{{x}^{2}}+bx+c=0$ is given by, $x=\frac{-b\pm \sqrt{{{b}^{2}}-4ac}}{2a}$ Compare $2{{x}^{2}}+3x-65=0$ with $a{{x}^{2}}+bx+c=0$ Here, $a=2,b=3$ and $c=-65$ Substitute the values of $a,b$ and $c$ in $x=\frac{-b\pm \sqrt{{{b}^{2}}-4ac}}{2a}$ $\begin{align} & x=\frac{-b\pm \sqrt{{{b}^{2}}-4ac}}{2a} \\ & =\frac{-3\pm \sqrt{{{3}^{2}}-4\cdot 2\cdot \left( -65 \right)}}{2\cdot 2} \\ & =\frac{-3\pm \sqrt{9+520}}{4} \\ & =\frac{-3\pm \sqrt{529}}{4} \end{align}$ $\begin{align} & x=\frac{-3\pm 23}{4} \\ & =\frac{-3+23}{4},\frac{-3-23}{4} \\ & =\frac{20}{4},\frac{-26}{4} \\ & =5,\frac{-13}{2} \end{align}$ Here, we only consider the positive value, x=5. Thus, the consecutive integers are 5, 6, and 7.
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