What is a Linear Function?

A linear function is a very important concept in math. Linear functions are used to draw straight-line graphs, and even elementary students can understand this concept easily. Let’s explain linear functions in a simple way!

Linear Function

What is a Function?

First, let’s talk about what a function is. A function is a rule that gives you one number when you put in another number. It’s like a vending machine: you put in a coin, and you get a drink. Think of a function as a machine with an input and an output.

What is a One-to-One Correspondence?

One-to-one correspondence means that each input is connected to exactly one output. For example, when you put a coin into a vending machine, you get exactly one drink. This means each input has one specific output.

Definition of a Linear Function

A linear function has the form ‘y = ax + b’. Here, ‘x’ and ‘y’ are placeholders for numbers, and ‘a’ and ‘b’ are numbers we choose. For example, ‘y = 2x + 3’ is a linear function.

Drawing the Graph

To understand a linear function, it’s helpful to draw a graph. Let’s take ‘y = 2x + 3’ as an example. First, we put different numbers into ‘x’ and find the corresponding ‘y’ values.


After finding these values, we plot the points on a graph, and we get a straight line. This is the key feature of a linear function.

What are Slope and Intercept?

In a linear function, ‘a’ is called the slope, and ‘b’ is called the intercept. Let’s explain these in simple terms!

What is Slope?

The slope shows how steep the graph is. Imagine a hill: if the hill is steep, it’s hard to climb. The slope is like that. In ‘y = 2x + 3’, the slope ‘a’ is 2. This means that for every 1 unit increase in x, y increases by 2 units.

What is Intercept?

The intercept is where the graph meets the y-axis. For example, in ‘y = 2x + 3’, when x is 0, y is 3. This point is the intercept. The intercept ‘b’ is 3, meaning the graph meets the y-axis at 3.

Graph Showing Slope and Intercept

The graph below shows the linear function ‘y = 2x + 3’ with the slope and intercept.

  1. Slope (a): Shows how steep the line is. Here, the slope ‘a’ is 2.
  2. Intercept (b): The point where the line meets the y-axis. Here, the intercept ‘b’ is 3.

Applications of Linear Functions

Linear functions are used in real life too. For example, calculating taxi fare often involves a base fare plus a distance-based fare. The base fare is ‘b’, and the distance fare is ‘a’.

Practice Problems

  1. What are the slope and intercept in ‘y = 3x + 2’?
  2. Find the value of ‘y’ when ‘x’ is 4.
  3. Draw the graph for ‘y = -x + 5’.


Linear functions might seem a bit tricky at first, but with practice, you’ll get the hang of it. By drawing graphs and understanding the slope and intercept, you can understand linear functions well. Keep practicing!

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