Mathematics
Grade 8
15 min
Rate of change
Rate of change
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1
Introduction & Learning Objectives
Learning Objectives
Define 'rate of change' and explain its meaning in the context of a function.
Calculate the rate of change from a table of values for a linear function.
Determine the rate of change from a graph of a linear function.
Calculate the rate of change given two points on a line.
Interpret the meaning of the rate of change in real-world scenarios.
Identify the rate of change (slope) in a linear equation written in slope-intercept form.
Have you ever thought about how quickly things change around you? 📈 From the speed of a car to the growth of a plant, change is everywhere!
In this lesson, you'll learn what 'rate of change' means in mathematics, especially when we talk about functions. Understanding rate of change helps us describe how...
2
Key Concepts & Vocabulary
TermDefinitionExample
Rate of ChangeThe rate of change describes how one quantity changes in relation to another quantity. It's often expressed as a ratio comparing the change in the dependent variable to the change in the independent variable.If a car travels 60 miles in 2 hours, its rate of change (speed) is 30 miles per hour.
SlopeFor linear functions, the rate of change is also known as the slope. It measures the steepness and direction of a line on a graph.A line that goes up from left to right has a positive slope, meaning a positive rate of change.
Linear FunctionA function whose graph is a straight line. Linear functions have a constant rate of change, meaning the rate of change never varies.The equation y = 2x + 3 represents a linear function because its graph is a straight...
3
Core Formulas
Rate of Change Formula (Slope Formula)
$$m = \frac{\text{Change in y}}{\text{Change in x}} = \frac{\Delta y}{\Delta x} = \frac{y_2 - y_1}{x_2 - x_1}$$
This formula is used to calculate the rate of change (or slope) between any two distinct points $(x_1, y_1)$ and $(x_2, y_2)$ on a line or in a data set. The 'm' typically represents the slope.
Slope-Intercept Form of a Linear Equation
$$y = mx + b$$
This is a common way to write the equation of a linear function. In this form, 'm' directly represents the rate of change (slope) of the line, and 'b' represents the y-intercept (where the line crosses the y-axis).
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Challenging
A gym membership costs a flat monthly fee plus an additional charge per fitness class. A member who took 4 classes was charged $50. A member who took 10 classes was charged $80. What is the rate of change (cost per class)?
A.$10 per class
B.$8 per class
C.$5 per class
D.$30 per class
Challenging
What is the rate of change for the linear function represented by the equation 4x + 2y = 10?
A.4
B.-2
C.2
D.5
Challenging
The rate of change between the points (a, 4) and (5, 16) is 3. What is the value of 'a'?
A.1
B.2
C.9
D.-1
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