Problem 60 - College Algebra and Calculus: An Applied Approach

Question

Find an equation of the line passing through the points. \((-8,0.6),(2,-2.4)\)

Step-by-Step Solution

Answer

The equation of the line passing through the points (-8,0.6) and (2,-2.4) is \(y = -3 / 10x - 1.8\)

Step 1: Find the Slope

Substitute the given points into the slope formula to find the slope of the line: \(m = (y_2 - y_1) / (x_2 - x_1) = (-2.4 - 0.6) / (2 - (-8)) = -3 / 10\)

Step 2: Substitute into Point-Slope Form

Substitute the slope \(m = -3 / 10\) and any given point, for instance, \((-8, 0.6)\) into the point-slope form \(y - y_1 = m(x - x_1)\) to get: \(y - 0.6 = -3 / 10 (x -(-8))\)

Step 3: Simplify the Equation

Simplify the equation obtained in Step 2 to get the equation of the line: \(y = -3 / 10x - 1.8\)

Key Concepts

Slope Formula

When dealing with linear functions, understanding the slope is crucial. The slope defines how steep a line is and the direction it's going. To calculate the slope (\textbf{m}), we use the slope formula:
\[ m = \frac{ y_2 - y_1 }{ x_2 - x_1 } \]
This formula simply requires the difference in y-coordinates (vertical change) divided by the difference in x-coordinates (horizontal change) between two points on the line. For example, using the points \((-8,0.6)\) and \( (2,-2.4) \), the slope is calculated as \[ m = \frac{-2.4 - 0.6}{2 - (-8)} = \frac{-3}{10} \]
The result tells us that for every 10 units we move horizontally, the line moves 3 units downward since the slope is negative.

Point-Slope Form

The point-slope form is an invaluable tool for writing the equation of a line when you have a point on the line and its slope. The generic formula is:
\[ y - y_1 = m(x - x_1) \]
Here, \(m\) is the slope and \((x_1, y_1)\) is the point through which the line passes. Using our slope of \( -\frac{3}{10} \) and the point \( (-8, 0.6) \) from the example, we insert these values into the formula:
\[-\frac{3}{10} (x - (-8)) = y - 0.6\]
The point-slope form gives us a direct way to write out the line's equation, which we can then simplify for our final expression.

Simplifying Equations

Simplifying equations is a process of rewriting them in a more 'digestible' form, often to express the equation as \(y = mx + b\), known as slope-intercept form. This process includes expanding brackets, combining like terms, and isolating the variable \(y\) on one side of the equation. To simplify the point-slope form obtained from the previous example:
\[ y - 0.6 = -\frac{3}{10}(x + 8) \]
We distribute the slope across the x-terms, combine like terms, and add \(0.6\) to both sides to isolate \(y\), arriving at:
\[ y = -\frac{3}{10}x - 1.8 \]
Simplification makes it easier to interpret and graph the equation because the slope (\(m\)) and the y-intercept (\(b\)) are clearly visible.

Linear Functions

Linear functions are fundamental in algebra and represent straight lines when graphed on a coordinate plane. Their general form is \(y = mx + b\) where \(m\) is the slope and \(b\) is the y-intercept—the point where the line crosses the y-axis. Key characteristics of linear functions include a constant rate of change (the slope) and the fact that they have no curves or angles in their graph.

Whenever you encounter two points, like \((-8,0.6)\) and \((2,-2.4)\), you can determine the equation of the line that connects these points by first finding the slope and then using either the point-slope or slope-intercept form to express the linear function that models the relationship between \(x\) and \(y\).