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The Slope of the Line y=mx+b

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Learning text on the topic The Slope of the Line y=mx+b

Slope of a Line – Definition

In everyday life, we encounter slopes from the steepness of a hill to the angle of a ramp. In mathematics, the slope of a line measures how steep a line is. It is often also referred to as the gradient.

The slope represents the steepness or incline of a line, defined as the ratio of the vertical change (rise) to the horizontal change (run) between two points on the line.

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Understanding Slope as a Rate of Change

The slope of a line is a measure of how one variable changes in relation to another. It's the same as a rate of change you might encounter in everyday life, such as speed.

The slope of a line can be an integer (whole number) or a fraction or decimal too. It can be positive to represent a line going upwards from left to right, or negative indicating a line that goes down from left to right. It is given by the value of mm in the equation of a straight line, y=mx+cy=mx+c.

For example, imagine you're on a road trip and want to calculate the average speed of your journey. Speed is a rate of change - it reflects how distance changes over time. In this case, the slope (speed) is the change in distance (rise) divided by the change in time (run).

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Graphing the Data:

  • Plot these points on a graph with 'Time' on the xx-axis and 'Distance' on the yy-axis.

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Finding the Slope (Speed):

  • Choose any two points on the graph. For example, (1,50)(1, 50) and (3,150)(3, 150).
  • Apply the slope formula: Slope (Speed) = (riserun\dfrac{\text{rise}}{\text{run}}) = (Change in DistanceChange in Time\dfrac{\text{Change in Distance}}{\text{Change in Time}})
  • Slope (Speed) = (15050)(31)=1002=50\frac{(150 - 50)}{(3 - 1)} = \frac{100}{2} = 50 miles per hour.

Equation of the Line:

  • The equation representing this relationship in the form y=mxy = mx could be written as Distance = 50×time50 \times{time}.
  • This equation tells us that for every hour of travel, the distance increases by 50 miles.

Understanding the concept of slope as a unit rate, like speed, helps make connections between mathematical concepts and real-world scenarios. It demonstrates how slope is not just a theoretical idea but a practical tool for everyday calculations.

Different Types of Slope

Type Of Slope Description Graph Example
Positive Slope Rises to the right, indicating the slope value is a positive number. As you move from left to right, the line goes up. 21604_TheSlopeOfTheLine-04.svg m=34m = \frac{3}{4}
Negative Slope Falls to the right, indicating the slope value is a negative number. As you move from left to right, the line goes down. 21604_TheSlopeOfTheLine-05.svg m=52m = \frac{-5}{2}
Zero Slope Represents a horizontal line, indicating the slope value is zero. There's no rise over the run. 21604_TheSlopeOfTheLine-17.svg m=0m = 0
Undefined Slope Represents a vertical line, indicating the slope is undefined because division by zero is not possible in mathematics. 21604_TheSlopeOfTheLine-06.svg Slope is undefined

Finding the Slope on a Graph – Step-By-Step Instructions and Examples

When looking at a graph, the slope (mm) is determined by how much the line rises (goes up or down) for every unit it runs (moves right). This can be visually represented and calculated as m=riserunm = \frac{\text{rise}}{\text{run}}.

Step Description Visual
Identify Points Locate the points on the graph. For this example, the points are (1,1)(1, 1) and (3,4)(3, 4). 21604_TheSlopeOfTheLine-09.svg
Rise and Run Observe the rise and run between the points. From 11 to 44 is a rise of 3 units (upwards), and from 11 to 33 is a run of 2 units (to the right). 21604_TheSlopeOfTheLine-09.svg
Slope Calculation Calculate the slope using the rise over run. The slope m=32m = \frac{3}{2}, indicating the line rises 3 units for every 2 units it moves to the right. 21604_TheSlopeOfTheLine-10.svg

Find the slope of the graphs.

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Finding the Slope When Given Two Points – Step-by-Step Instructions

To calculate the slope, use the formula m=y2y1x2x1m = \frac{y_2 - y_1}{x_2 - x_1} when you know at least two points on the line. This formula makes it easy to see how steep a line is without a protractor.

What is the slope of the line that passes through the points (6,3)(6, -3) and (2,7)(2, 7)?

To calculate the slope of a line given two points, (x1,y1)(x_1, y_1) and (x2,y2)(x_2, y_2), we use the slope formula:

21604_TheSlopeOfTheLine-14.svg

Step 1: Identify the coordinates of the two points.

Point 1: (6,3)(6, -3), where x1=6x_1 = 6 and y1=3y_1 = -3

Point 2: (2,7)(2, 7), where x2=2x_2 = 2 and y2=7y_2 = 7

Step 2: Plug the coordinates into the slope formula.

m=7(3)26m = \frac{7 - (-3)}{2 - 6}

It is important to do the calculation in the correct order as mixing up the positions of the xx and yy values in the formula can result in different answers to the one we want!

Step 3: Perform the subtraction in the numerator and the denominator.

m=7+326m = \frac{7 + 3}{2 - 6}

m=104m = \frac{10}{-4}

Step 4: Simplify the fraction.

m=52m = -\frac{5}{2}

Therefore, the slope of the line passing through the points (6,3)(6, -3) and (2,7)(2, 7) is 52-\frac{5}{2}.

This negative slope indicates that the line falls as it moves from left to right.

Try some on your own!

Computing the slope of a line can be useful when analysing data and identifying patterns.

Finding the Slope from an Equation

Understanding how to find the slope from an equation involves recognising the slope-intercept form of a line, which is expressed as y=mx+cy = mx + c. In this form, mm represents the slope of the line, indicating how steep it is and in which direction it tilts. The cc value represents the y-intercept, where the line crosses the y-axis.

The slope-intercept form y=mx+cy = mx + c provides a straightforward way to identify the slope directly from the equation of a line. The coefficient of xx (that is, mm) is the slope. This tells us by how many units yy changes for every one-unit increase in xx.

Consider the equation of a line y=2x+3y = 2x + 3.

  • Identify the Slope: In the equation y=2x+3y = 2x + 3, the coefficient of xx is 22. This means the slope (mm) of the line is 22.

  • Interpret the Slope: A slope of 22 means that for every one unit the xx value increases, the yy value increases by 22 units. This indicates the line rises to the right.

The Slope of a Line – Practice Questions

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The Slope of a Line – Summary

Key Learnings from this Text:

  • The slope of a line tells us how steep it is by comparing the vertical change to the horizontal change between two points.

  • Slope is directly related to the rate of change, similar to everyday concepts like speed. It shows how quickly one thing changes in relation to another.

  • You can find the slope by using the formula m=y2y1x2x1m = \frac{y_2 - y_1}{x_2 - x_1}, which helps us understand the line's incline without needing any special tools.

  • By looking at a graph, we can visually determine the slope by identifying the rise and run between two points. This visual approach makes it easier to understand the concept of slope.

  • Understanding slope is crucial for solving real-life problems, from designing ramps to calculating how fast an object moves. It's a practical skill that connects classroom math to the world around us.

Having a solid understanding of the slope of a line will be helpful with graphing linear equations, and solving systems of equations by graphing.

The Slope of a Line – Frequently Asked Questions

The Slope of the Line y=mx+b exercise

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