Intermediate Algebra: Connecting Concepts through Application

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

Chapter 1 - Linear Functions - 1.5 Finding Equations of Lines - 1.5 Exercises - Page 76: 44

Answer

$\color{blue}{y=-2.5x+17}$

Work Step by Step

Recall: (1) The slope $m$ of a line passing through points $(x_1, y_1)$ and $(x_2, y_2)$ is given by the formula $$m=\dfrac{y_2-y_1}{x_2-x_1}$$ (2) The slope-intercept form of a line's equation is $y=mx+b$ where $m$=slope and $(0, b)$ is the $y$-intercept. Solve for the slope of the line using the formula above and the points $(4, 7)$ and $(14, -18)$: \begin{align*} m&=\frac{y_2-y_1}{x_2-x_1}\\ m&=\frac{-18-7}{14-4}\\\\ m&=\frac{-25}{10}\\\\ m&=-2.5 \end{align*} Hence, the tentative equation fo the line that contains the given points is: $$y=-2.5x+b$$ Solve for the $b$ by substituting the $x$ and $y$ values of the point $(4, 7)$ into the tentative equation above to obtain: \begin{align*} y&=-2.5x+b\\ 7&=-2.5(4)+b\\ 7&=-10+b\\ 7+10&=b\\ 17&=b\\ \end{align*} Therefore, the equation of the line that contains the given points in the table is $\color{blue}{y=-2.5x+17}$.
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