Big Ideas Math: Modeling Real Life, Grade 8
BI
Big Ideas Math: Modeling Real Life, Grade 8 View details
3. Graphing Proportional Relationships
Continue to next subchapter

Exercise 12 Page 159

When two quantities x and y are proportional, the relationship can be represented by the equation y=mx.

Proportional Relationship: Yes.
Equation: y= 13x

Practice makes perfect

Consider the given ratio table.

x 3 6 9 12
y 1 2 3 4
The value of x and its corresponding value of y represents an ordered pair that can be plotted in a coordinate plane. Let's plot the ordered pairs and draw a line through the points.
We want to find if x and y are in a proportional relationship. To do so, remember that when two quantities are proportional, the relationship can be represented by the following equation. y=mx Here, m is the constant of proportionality. The graph of this equation is a line with a slope m that passes through the origin. Notice that our line pass through the origin. This means that x and y are in a proportional relationship. To find the equation of the line, we will use the Slope Formula to obtain m. m=y_2-y_1/x_2-x_1 Let's use the points ( 0, 0) and( 3, 1) in the Slope Formula.
m=y_2-y_1/x_2-x_1
m=1- 0/3- 0
m=1/3
Finally, we can substitute the slope into the equation of the proportional relationship. y=1/3x

Extra

Linear Equations

A linear equation is an equation whose graph is a line.

This type of equation contains at least one linear term and any number of constants. Let's see a few examples! & y=2x+1, & 3x=6 +3, & 2y+x=4 For those of you who are interested in learning more about the different types of linear equations and their graphs, you can read more about them on the following pages.