# Lesson video

In progress...

In this lesson we're going to be calculating the number of sides that a polygon has when we're given the sum of interior angles.

A polygon has interior angles that sum to 540 degrees.

We've been asked to work out the number of sides that the polygon has.

The sum of interior angles can be found by calculating n subtract two multiplied by 180, where n is the number of sides.

If we substitute 540 into this formula we have this equation.

To begin solving it we're going to divide both sides by 180.

This gives us three is equal to n subtract two.

The inverse of subtracting two is adding two.

So let's add two to both sides.

This gives n equals five.

N is the number of sides, so this polygon has five sides.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

To find the number of sides you need to divide the sum of interior angles by 180 and then add two.

The regular polygon had interior angles that summed to 540 degrees.

A regular polygon has all angles that are equal.

The first thing we need to do in order to find the size of each interior angle is to calculate the number of sides that this regular polygon has.

The sum of interior angles is worked out by calculating n subtract two multiplied by 180, where n is the number of sides.

So 540 is equal is to n subtract two multiplied by 180.

Using inverse operations we're going to solve this equation to find n, which is the number of sides.

First, let's divide both sides by 180.

This means that three is equal to n subtract two.

Next, we're going to add two to both sides.

So our regular polygon has five sides.

To find the size of each interior angle we're going to divide 540 by five.

This gives us 108 degrees.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Once you have found the number of sides that each polygon has divide the sum of interior angles by this.

The regular polygon had interior angles that summed to 540 degrees.

We've been asked to work out the size of each exterior angle.

So the first thing we need to do is to work out the number of sides that this regular polygon has.

Interior angles of a polygon are calculated by doing n subtract two multiplied by 180, where n is the number of sides.

We know that the interior angles in our regular polygon sum to 540.

So 540 is equal to n subtract two multiplied by 180.

Using inverse functions we're going to solve this equation to find that the regular polygon has five sides.

Exterior angles are calculated by dividing 360 by the number of sides, as in a regular polygon all exterior angles are equal and sum to 360.

We're going to do 360 divided by five, which gives us the exterior angle of 72 degrees.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.