Problem 16 - Algebra 1

Question

Write an equation of the line that passes through the given points. $$ (3,-12),(8,4) $$

Step-by-Step Solution

Answer

The equation of the line is \(y = 3.2x - 21.6\)

Step 1: Find the Slope

The slope (m) of a line passing through the points (x1,y1) and (x2,y2) is given by the formula m = (y2 - y1) / (x2 - x1). For the points (3,-12) and (8,4), this becomes m = (4 - -12) / (8 - 3) = 16 / 5 = 3.2.

Step 2: Use the Point-Slope Form to Write the Equation of the Line

The point-slope form of a line's equation is y - y1 = m(x - x1). Substitute m = 3.2 from step 1 and the coordinates of one of the points. If we take the point (3,-12), the equation becomes y - (-12) = 3.2(x - 3).

Step 3: Rewrite in Slope-Intercept Form

To rewrite the equation in slope-intercept form (i.e., y=mx+b), carry out the multiplication on the right side, and simplify to yield final equation, y = 3.2x - 21.6.

Key Concepts

Slope Calculation

Understanding how to calculate the slope of a line is critical in algebra, particularly when dealing with linear equations. The slope is a measure of how steep a line is and is represented by the letter 'm'. In a two-dimensional space, the slope is the ratio of the vertical change (rise) to the horizontal change (run) between two distinct points on the line.

To find the slope between two points, \( (x_1, y_1) \) and \( (x_2, y_2) \) on a graph, we use the following formula:
\[ m = \frac{y_2 - y_1}{x_2 - x_1} \]
For the given points \( (3, -12) \) and \( (8, 4) \), we calculate the slope as follows:
\[ m = \frac{4 - (-12)}{8 - 3} = \frac{16}{5} =3.2 \]
This value tells us that for every five units we move horizontally to the right along the line, the line itself rises by 16 units. The sign of the slope indicates the line's direction; a positive slope means the line ascends from left to right, while a negative slope implies descent.

Point-Slope Form

After calculating the slope, we can write the equation of a line using the point-slope form, which is especially useful when we have one point on the line and the slope. The point-slope form is given by:
\[ y - y_1 = m(x - x_1) \]
Here, \( (x_1, y_1) \) is a known point on the line, and 'm' is the slope. This form directly shows how the slope and a single point define the line.

Using the example with our calculated slope of 3.2 and the point \( (3, -12) \) we get:
\[ y - (-12) = 3.2(x - 3) \]
By applying the point-slope form, we establish the foundation for expressing the linear equation in various forms, including the commonly used slope-intercept form. It's worth noting that this equation is a direct translation from the slope definition and the given point.

Slope-Intercept Form

The slope-intercept form is the most recognized format for a linear equation and is expressed as \( y = mx + b \), where 'm' is the slope and 'b' is the y-intercept. The y-intercept is the point where the line crosses the y-axis. This form allows us to quickly understand both the steepness of the line and where it intersects the y-axis.

To convert the point-slope form equation to slope-intercept form from our previous point-slope example, we follow these steps:
- Multiply out the right side of the point-slope equation
- Simplify and solve for 'y'
The result for our line is:
\[ y = 3.2x - 21.6 \]
This equation makes it simple to graph the line or to calculate the y-value for any x-value on the line. The slope-intercept form also simplifies the process of comparing two lines for parallel or perpendicular orientation since their slopes can be easily contrasted.