# Introduction to Linear Functions

Definition: A linear function is a function whose points form a straight line when graphed. The equation takes the form or . A linear function is a polynomial of degree 1.

# Arithmetic Sequences

An arithmetic sequence is an example of a function whose points lie on a straight line.

In general, the domain of an arithmetic sequence is the set of natural numbers . The range is the set of terms in the sequence.

When graphed, the points in the sequence lie on a straight line. There are no intermediate points, so we don’t draw a line through these points.

The general term for the sequence graphed here is .

Review how to find the general term for an arithmetic sequence from the graph here.

# From Arithmetic Sequences to Linear Functions

The structure of the formula for arithmetic sequences and linear functions is identical. Instead of variables (place value) and (term value), we use the generic labels and . Instead of for common difference – the amount the sequence increases each term – we use for ‘slope’ or ‘gradient’ which is the amount the line goes up for one whole unit right.

When studying linear functions in general, we assume the domain is the set of all possible numbers, that is, every value on the axis. We say “ is a member of the set of real numbers”, and we write . The range is also all possible numbers. To express the range we write .

Check out the similarities and differences in this applet:

# Applications

A linear function can be used to apply math to any data set where there is a steady increase or decrease, or an approximately steady increase or decrease. Linear functions are also used extensively in the study of calculus.

Example 1: Pay

When a person is being paid by the hour, they might work 1, 2, 3, …10 hours (like an arithmetic progression), however if they work 3.25 hours they will be paid for the ‘0.25’. Here is the example of the appliance repair technician from unit 5.