Try sofatutor for 30 Days

Discover why over 1.6 MILLION pupils choose sofatutor!

The Slope of the Line y=mx+b

Do you want to learn faster and more easily?

Then why not use our learning videos, and practice for school with learning games.

Try for 30 Days

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.

21604_TheSlopeOfTheLine-01.svg

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 $m$ in the equation of a straight line, $y=mx+c$.

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).

27728_TheSlopeOfTheLine-02.svg

Graphing the Data:

  • Plot these points on a graph with 'Time' on the $x$-axis and 'Distance' on the $y$-axis.

21604_TheSlopeOfTheLine-03.svg

Finding the Slope (Speed):

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

Equation of the Line:

  • The equation representing this relationship in the form $y = mx$ could be written as Distance = $50 \times{time}$.
  • 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 $m = \frac{3}{4}$
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 $m = \frac{-5}{2}$
Zero Slope Represents a horizontal line, indicating the slope value is zero. There's no rise over the run. 21604_TheSlopeOfTheLine-17.svg $m = 0$
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 ($m$) 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 $m = \frac{\text{rise}}{\text{run}}$.

Step Description Visual
Identify Points Locate the points on the graph. For this example, the points are $(1, 1)$ and $(3, 4)$. 21604_TheSlopeOfTheLine-09.svg
Rise and Run Observe the rise and run between the points. From $1$ to $4$ is a rise of 3 units (upwards), and from $1$ to $3$ 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 $m = \frac{3}{2}$, 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.

21604_TheSlopeOfTheLine-11.svg

Given a graph where a line passes through the points $(-4, -2)$ and $(-1, 2)$, what is the slope of this line?

21604_TheSlopeOfTheLine-12.svg

Given a graph where a line passes through the points $(2, 8)$ and $(5, 3)$, what is the slope of this line?

21604_TheSlopeOfTheLine-13.svg

Given a graph where a line passes through the points $(1, -5)$ and $(4, -1)$, what is the slope of this line?

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

To calculate the slope, use the formula $m = \frac{y_2 - y_1}{x_2 - x_1}$ 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 $(6, -3)$ and $(2, 7)$?

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

21604_TheSlopeOfTheLine-14.svg

Step 1: Identify the coordinates of the two points.

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

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

Step 2: Plug the coordinates into the slope formula.

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

It is important to do the calculation in the correct order as mixing up the positions of the $x$ and $y$ 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.

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

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

Step 4: Simplify the fraction.

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

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

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

Try some on your own!

Given two points on a line, $(1, 2)$ and $(3, 8)$, what is the slope of the line?
If you have the points $(4, -1)$ and $(2, -5)$ on a graph, what is the slope of the line connecting these points?
How do you find the slope of a line that passes through the points $(-2, 3)$ and $(-2, -4)$?
Given two points on a line, $(-1, 4)$ and $(3, 0)$, what is the slope of the line?
What is the slope of the line that connects the points $(2, 3)$ and $(5, -1)$?
What is the slope of the line that goes through the points $(5, 5)$ and $(10, 15)$?

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 $y = mx + c$. In this form, $m$ represents the slope of the line, indicating how steep it is and in which direction it tilts. The $c$ value represents the y-intercept, where the line crosses the y-axis.

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

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

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

  • Interpret the Slope: A slope of $2$ means that for every one unit the $x$ value increases, the $y$ value increases by $2$ units. This indicates the line rises to the right.

What is the slope of the line described by the equation $y = -3x + 1$?
Given the equation $y = \frac{1}{2}x - 4$, identify the slope of the line.
Find the slope of the line with the equation $y = 5x$.
If a line is described by the equation $y = -\frac{4}{5}x + 2$, what is its slope?

The Slope of a Line – Practice Questions

21604_TheSlopeOfTheLine-15.svg

Consider a graph where a line passes through $(0, -2)$ and $(3, 4)$. Calculate the slope of this line.
Given the equation $y = -\frac{3}{2}x + 3$, what is the slope of the line?

21604_TheSlopeOfTheLine-16.svg

A line on a graph crosses through the points $(-5, 3)$ and $(-2, -3)$. What is the slope of this line?
What is the slope of a line that is described by the equation $y = 3x - 6$?
If a line in a graph goes through the points $(6, 2)$ and $(10, -6)$, calculate its slope.
Given the line's equation as $y = \frac{2}{3}x + 1$, identify the slope.

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 $m = \frac{y_2 - y_1}{x_2 - x_1}$, 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

What is the slope of a line?
How do you calculate the slope with two points?
What does a positive slope indicate?
What does a negative slope indicate?
What is a zero slope?
What does an undefined slope mean?
Can the slope formula be used for any type of line?
How does the slope relate to the equation of a line?
What does it mean for two lines to be parallel in terms of slope?
How do slopes of perpendicular lines relate to each other?

The Slope of the Line y=mx+b exercise

Would you like to apply the knowledge you’ve learnt? You can review and practice it with the tasks for the learning text The Slope of the Line y=mx+b.
  • Identify the gradient of a straight line.

    Hints

    The gradient or steepness of the straight line is measured by the difference in $y$ divided by the difference in $x$.

    We use the formal way to write it like this:

    $y = mx + c$

    • $m$ represents the gradient (steepness of the slope)
    • $c$ represents the $y$ intercept (where the line crosses the $y$ axis)

    We are looking for $m$, the coefficient of $x$.

    In this example, $y = 2x - 4$, the gradient $m = 2$

    Solution

    The answer is $3$.

    The line $\textbf{y = 3x + 6}$ is in the form $y = mx + c$, where $m$ is the gradient of the line and $c$ is the $y$-intercept. This is shown on the diagram.

  • Identify the $y$-intercept.

    Hints

    We are looking for the $y$-intercept. This is where the straight line cuts the $y$ axis.

    A straight line graph is written in the form:

    Sometimes it is written in a different order. For example, $y = 6 + 7x$, but the $y$-intercept is still the number by itself. The coefficient of $x$ is the gradient.

    In the straight line $y = 2x - 8$, the $y$ intercept is $-8$.

    Solution
    • $y = 2x + 3$, the $y$ intercept, $c = 3$.
    • $y = 3x - 2$, the $y$ intercept, $c = -2$.
    • $y = 4x - 3$, the $y$ intercept, $c = -3$.
    • $y = 4 + 2x$, the $y$ intercept, $c = 4$.
  • Find the equation of the straight line.

    Hints

    To work out the equation of the line we use $y = mx + c$.

    • $m =$ gradient or steepness of the line.
    • $c =$ the $y$-intercept (where the line cuts the $y$ axis).

    To find the gradient, we use a triangle to find the change in $y$ divided by the change in $x$.

    The $y$-intercept it is where the line crosses through the $y$ axis.

    See the example.

    Solution

    $y = -2x + 3$

    • The $y$-intercept, $c$ is $3$.
    • the gradient, $m = \frac{-2}{1} = -2$.
  • Calculate the gradient of a straight line.

    Hints

    To work out the gradient rearrange the equation to the form $y = mx + c$.

    Rearrange the equation. For example,

    Solution

    Gradient $= 3$

    Rearrange the equation to the form $y = mx + c$.

    $m =$ gradient.

  • What is the gradient?

    Hints

    The gradient is the steepness of the line.

    • Drop a triangle under the line.
    • Find the distance in $y$ divided by the distance in $x$.

    Here is an example of how to work out the gradient.

    • We draw a triangle under the line.
    • Change in $y = 6$.
    • Change in $x = 2$.
    • $\frac{6}{2} = 3$.

    For this question we could use the triangle shown.

    Divide the change in $y$ by the change in $x$ to get the gradient.

    Solution

    Gradient $= 2$.

    • We draw a triangle under the line.
    • Change in $y = 4$.
    • Change in $x = 2$.
    • $\frac{4}{2} = 2$.
  • Find the straight line graph.

    Hints

    The equation must be rearranged into the form $y = mx + c$ in order to find the correct gradient, $m$ and correct $y$-intercept, $c$.

    For example,

    When the equation is in the form $y = mx + c$, we are looking for a graph which has a $y$-intercept of the value of $c$ and a gradient of the value of $m$.

    For example, $y = 6x + 7$ has a $y$-intercept of $7$ and a gradient of $6$.

    Solution

    $y = 2x + 1$

Rating

Be the first to give a rating!
The authors
Avatar
sofatutor Team