Mathematics
Grade 9
15 min
Find the slope of a graph
Find the slope of a graph
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1
Introduction & Learning Objectives
Learning Objectives
Define slope as the ratio of vertical change to horizontal change.
Visually identify whether the slope of a line is positive, negative, zero, or undefined.
Calculate the slope of a line from a graph by counting the 'rise' and 'run'.
Determine the coordinates of two points on a line and use the slope formula to calculate the slope.
Explain the relationship between the steepness of a line and the absolute value of its slope.
Interpret the slope as a rate of change in a real-world context represented by a graph.
Ever wondered how engineers design a roller coaster's thrilling drops or a safe wheelchair ramp? 🎢 It all comes down to understanding steepness!
In this tutorial, you will learn how to measure the steepness of a line on a g...
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Key Concepts & Vocabulary
TermDefinitionExample
SlopeA number that measures the steepness and direction of a line. It is the ratio of the vertical change (the rise) to the horizontal change (the run) between any two points on the line.A slope of 2 means that for every 1 unit you move to the right on the graph, you must move 2 units up.
RiseThe vertical change between two points on a line. It can be positive (up) or negative (down).If you move from the point (1, 2) to (3, 7), the rise is 7 - 2 = 5.
RunThe horizontal change between two points on a line. It can be positive (right) or negative (left).If you move from the point (1, 2) to (3, 7), the run is 3 - 1 = 2.
Positive SlopeA line that goes upward from left to right. This indicates a positive rate of change.A graph showing the distance you travel over time as yo...
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Core Formulas
Rise Over Run Formula
m = \frac{\text{rise}}{\text{run}}
Use this when you can easily count the vertical and horizontal units between two points directly on the graph. It's a visual method.
Slope Formula
m = \frac{y_2 - y_1}{x_2 - x_1}
Use this when you have the coordinates of any two points on the line, (x₁, y₁) and (x₂, y₂). This is the most reliable algebraic method.
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Challenging
Two lines, L₁ and L₂, have slopes m₁ and m₂, respectively. If it is known that |m₁| > |m₂|, what can be definitively concluded?
A.Line L₁ is steeper than line L₂.
B.Line L₁ has a positive slope and L₂ has a negative slope.
C.Line L₁ is longer than line L₂.
D.The y-intercept of L₁ is greater than the y-intercept of L₂.
Challenging
A line passes through points (a, b) and (c, d), where a ≠ c. If the slope is a negative number whose absolute value is less than 1 (e.g., -1/2), what must be true about the relationship between the absolute vertical change |d - b| and the absolute horizontal change |c - a|?
A.The absolute vertical change is equal to the absolute horizontal change.
B.The absolute vertical change is less than the absolute horizontal change.
C.The absolute vertical change is greater than the absolute horizontal change.
D.The relationship cannot be determined.
Challenging
A graph shows a company's profit. The slope between Year 1 and Year 2 is 2. The slope between Year 2 and Year 3 is 0. The slope between Year 3 and Year 4 is -1.5. Which statement is the best interpretation?
A.The company's profit grew fastest between Year 3 and Year 4.
B.The company's profit was constant between Year 1 and Year 2.
C.The company's profit grew between Year 1 and 2, then stayed the same, then decreased.
D.The company lost money every year.
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