Linear Function

A linear function, as it is called, is an algebraic expression that represents the graph of a straight line.

When we talk about functions, it's important to highlight that the graphs of functions are represented in an axis system where there is a horizontal axis $X$ and a vertical axis $Y$ .

Linear functions can be expressed by the expressions $y = mx$ or $y = mx + b$ , where m represents the slope of the line while $b$ (when it exists) represents the y-intercept.

To plot a linear function, all we need are $2$ points. If the linear function is given, you can substitute a value for $X$ and obtain the corresponding $Y$ value.

Detailed explanation

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Test yourself on linear functions!

For the function in front of you, the slope is?

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A linear function is from the family of functions $Y=mx+b$ and represents a straight line.

$m$

We mark the slope of the function: positive or negative.

$m>0$ : upward sloping line

$m<0$ : downward sloping line

$m=0$ : a line parallel to the $X$ axis.

$b$

Marks the point where the function intersects the $Y$ axis.

Important points:

For every value of $X$ , the function will return a value of $Y$ .

The linear function is a straight line that is either ascending, descending, or parallel to the $X$ axis, but never parallel to the $Y$ axis.

Let's observe the line from left to right.

Different Representations of Linear Functions

$Y=mx+b$ : standard representation

$Y=mx$ : (when $b=0$ , the line cuts the $Y$ axis at the origin, when $Y=0$ )

$Y=b$ (when $m=0$ , the slope of the line is $0$ and therefore parallel to the $X$ axis)

Pay attention:

Sometimes, you'll find an equation that is not arranged and looks like this $mx-y=b$

This is also a linear function. Simply isolate $Y$ and see how it comes to the standard representation.

Sometimes, $X$ will be divided by some number $C$ :

$Y=\frac{mx}{c}+b$

This equation also represents a linear function.

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Test your knowledge

Question 1

For the function in front of you, the slope is?

Question 2

For the function in front of you, the slope is?

Question 3

For the function in front of you, the slope is?

When is a function not a linear function?

When $X$ is raised to a power: $Y=X^2$
When there is a square root for: $Y=\sqrt{X}$
When there is no $Y: X=b$

Graphical Representation of a Function that Depicts a Straight-Line Relationship

The linear function will appear as a straight line that is ascending, descending, or parallel to the $X$ axis but never parallel to the $Y$ axis.

For each value of $X$ , we will obtain only one value of $Y$ and vice versa.

We observe the line from left to right to see whether it ascends or descends.

Want to know more? Check out this article.

The concept of slope in the function $y=mx$

$M$ represents the slope of the function for us and determines whether the straight line goes up, goes down, or is parallel to the $X$ axis.

The linear function $y=mx+b$

The linear function represents a straight line where $M$ represents the slope and $b$ represents the y-intercept of the line with the $Y$ axis.

Do you know what the answer is?

Question 1

For the function in front of you, the slope is?

Question 2

For the function in front of you, the slope is?

Question 3

For the function in front of you, the slope is?

Finding the Equation of a Straight Line

We can find the equation of a straight line in 5 ways:

Using slope and a point
With the help of 2 points the line passes through.
Using parallel lines.
With the help of perpendicular lines.
With the help of a graph.

Want to learn more? Check out this article.

Positivity and Negativity of a Function

The function is positive when it is above the $X$ axis when $Y>0$

Find the values of $X$ for which the function takes on positive Y values.

The function is negative when it is below the $X$ axis as $Y>0$

Find the values of $X$ for which the function takes on negative $Y$ values.

Want to know more? Check out this article.

Check your understanding

Question 1

For the function in front of you, the slope is?

Question 2

For the function in front of you, the slope is?

Question 3

For the function in front of you, the slope is?

Representation of Phenomena Using Linear Functions

A linear function describes the relationship between $X$ and $Y$ .

Therefore, we can represent different phenomena with the help of a linear function.

We will understand what graph represents each situation and draw the correct conclusions.

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Inequality

We can solve inequalities between linear functions in two ways:

Using the given equations and with the help of graphical representations.

Want to know more? Check out this article.

Do you think you will be able to solve it?

Question 1

What is the solution to the following inequality?

$$ 10x-4\leq-3x-8 $$

Question 2

Look at the linear function represented in the diagram.

When is the function positive?

Question 3

Look at the function shown in the figure.

When is the function positive?

Let's illustrate this with an example.

Given the function: $y = 2x + 1$

We are asked to graph it on the coordinate system.

As we have discussed, to do this we need two points, which we will place in the function's expression. Choose any two points we like, it doesn't matter.

Now we will plot the two points on the coordinate system and connect them. This is actually a graph of the function for $y=2x+1$ .

Examples and Exercises with Solutions for Linear Functions

Exercise #1

For the function in front of you, the slope is?

Video Solution

Step-by-Step Solution

To solve this problem, we need to determine the slope of the line depicted on the graph.

First, understand that the slope of a line on a coordinate plane indicates how steep the line is and the direction it is heading. Specifically:

A positive slope means the line rises as it goes from left to right.
A negative slope means the line falls as it goes from left to right.

Let's examine the graph given:

We see that the line starts at a higher point on the left and descends to a lower point on the right side.
As we move from the left side of the graph towards the right, the line goes downwards.

This downward trajectory clearly indicates a negative slope because the line is declining as we move horizontally left to right.

Therefore, the slope of this function is Negative.

The correct answer is, therefore, Negative slope.

Answer

Negative slope

Exercise #2

For the function in front of you, the slope is?

Video Solution

Step-by-Step Solution

To solve this problem, let's analyze the given graph of the function to determine the slope's sign.

The slope of a line on a graph indicates the line's direction. A line with a positive slope rises as it moves from left to right, indicating that for every step taken to the right (along the x-axis), we move upward. Conversely, a line with a negative slope falls as it moves from left to right, meaning each step to the right results in moving downward.

Examining the graph provided, the red line starts higher on the left and goes downward towards the right visually. This indicates that the line is rising as it goes from left to right, which confirms it has a positive slope.

Therefore, the solution to the problem, regarding the slope of the line, is that it is a Positive slope.

Answer

Positive slope

Exercise #3

For the function in front of you, the slope is?

Video Solution

Step-by-Step Solution

To solve this problem, let's evaluate the graph of the line provided:

The line is visually represented as starting from the bottom left to the top right, moving upwards.
In a standard Cartesian graph, a line that ascends as it progresses from left to right implies a positive change in the y-coordinate as the x-coordinate increases.
This upward trajectory indicates that the slope, $m$ , is positive.

Thus, the slope of the function is positive.

Therefore, the answer is Positive slope.

Answer

Positive slope

Exercise #4

For the function in front of you, the slope is?

Video Solution

Step-by-Step Solution

To determine the slope of the line, we'll examine the direction of the line segment on the graph:

The line depicted moves from the top left, passing through a point with higher $y$ -coordinate values, to the bottom right, ending at a point with lower $y$ -coordinate values.
This movement indicates that as $x$ increases (the direction to the right along the $x$ -axis), the $y$ -coordinate decreases.
When the $y$ -value reduces as the $x$ -value grows, the slope $m$ is negative.

Since the line descends from left to right, the slope of the line is negative.

Therefore, the slope of the function is a negative slope.

Answer

Negative slope

Exercise #5

For the function in front of you, the slope is?

Video Solution

Step-by-Step Solution

To solve this problem, follow these steps:

Step 1: Observe the given graph and the plotted line.
Step 2: Determine the direction of the line as it moves from left to right across the graph.
Step 3: Understand that a line moving downwards from left to right represents a negative slope.

Now, let's work through these steps:

Step 1: The graph shows a straight line that starts higher on the left side and descends towards the right side.

Step 2: As the line moves from left to right, it descends. This is a key indicator of the slope type.

Step 3: A line that moves downward from the left side to the right side of the graph (decreasing in height as it proceeds to the right) is characteristic of a negative slope. Conversely, a positive slope would show a line ascending as it moves rightward.

Therefore, the solution to the problem is the line has a negative slope.

Answer

Negative slope

Test your knowledge

Question 1

Given the linear function:

$$ y=x-4 $$

What is the rate of change of the function?

Question 2

Given the linear function:

$$ y=1-4x $$

What is the rate of change of the function?

Question 3

For the function in front of you, the slope is?

Start practice

Linear Function

Test yourself on linear functions!

Linear Function

$m$

$b$

Different Representations of Linear Functions

When is a function not a linear function?