Year 9 Interactive Maths - Second Edition

Linear Functions

If the power of both x and y in a relation is one, then the relation is called a linear relation or linear function.

For example, y = 3x + 5, 7x – 8y = 56 and 2x + 3y + 6 = 0 are linear functions because the power of both x and y is one.

Plotting Graphs of Linear Functions

To plot a linear graph of a linear function, plot a number of ordered pairs; and then join these points with a ruler.

Example 1

Plot the graph of  y = 2x + 3.

Solution:

Note:

The graph is a straight line sloping upwards to the right as the value of x increases.

Example 2

Solution:

Note:

The graph is a straight line sloping downwards to the right as the value of x increases.

Key Terms

linear function, linear relation, linear graph