Mathematics
Grade 8
15 min
Interpret linear functions
Interpret linear functions
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1
Introduction & Learning Objectives
Learning Objectives
Identify the slope and y-intercept of a linear function from equations, graphs, and tables.
Explain the meaning of the slope as a rate of change in real-world contexts.
Explain the meaning of the y-intercept as an initial value or starting point in real-world contexts.
Relate the independent and dependent variables to the context of a linear function.
Use interpretations of slope and y-intercept to answer questions about real-world scenarios.
Compare and contrast different linear functions based on their contextual interpretations.
Ever wonder how scientists predict the path of a hurricane or how much money you'll save over time? 🌀 Linear functions help us understand these patterns!
In this lesson, you'll learn how to 'read between the li...
2
Key Concepts & Vocabulary
TermDefinitionExample
Linear FunctionA relationship between two variables that, when graphed, forms a straight line. It describes a constant rate of change.The relationship between the number of hours worked and the money earned, if you get paid a fixed amount per hour.
Slope (m)The measure of the steepness of a line, representing the rate of change of the dependent variable with respect to the independent variable. It's often described as 'rise over run'.If a car travels at 60 miles per hour, the slope is 60 miles/hour, meaning for every 1 hour, the distance increases by 60 miles.
Y-intercept (b)The point where the line crosses the y-axis. It represents the value of the dependent variable when the independent variable is zero.In a savings account, the initial deposit is th...
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Core Formulas
Slope Formula
$m = \frac{y_2 - y_1}{x_2 - x_1}$
Used to calculate the slope (rate of change) of a line given any two points $(x_1, y_1)$ and $(x_2, y_2)$ on the line.
Slope-Intercept Form
$y = mx + b$
A common way to write linear equations, where 'm' is the slope and 'b' is the y-intercept. This form makes it easy to identify these key features.
Interpreting Slope in Context
For every 1 unit increase in the independent variable (x), the dependent variable (y) changes by 'm' units.
This rule helps translate the numerical value of the slope into a meaningful statement about the relationship between the quantities in a real-world problem, including units.
Interpreting Y-intercept in Context
When the independent variable (x) is 0, the...
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Challenging
Gym A charges a $40 sign-up fee and $20 per month. Gym B charges no sign-up fee and $30 per month. After how many months will the total cost for both gyms be the same?
A.2 months
B.4 months
C.6 months
D.8 months
Challenging
A new business's profit, P, in thousands of dollars, is modeled by the equation P = 10t - 50, where t is the number of months in operation. What is the real-world meaning of the y-intercept?
A.The business started with a debt of $50,000.
B.The business loses $50,000 each month.
C.It will take 50 months for the business to make a profit.
D.The business's maximum possible loss is $50,000.
Challenging
A submarine is ascending to the surface. Its depth is a linear function of time. After 3 minutes, its depth is 350 meters. It is ascending at a constant rate of 50 meters per minute. What was the submarine's initial depth when it began its ascent?
A.200 meters
B.350 meters
C.450 meters
D.500 meters
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