In this activity, we will be learning to identify triangles using information about their angles. 

 

Remember that the interior angles of a triangle add up to 180º

 

A right-angled triangle has one 90º angle.

 

An isosceles triangle has two equal angles.

 

An equilateral triangle has three equal angles, each of size 60º

 

A scalene triangle has no equal angles.

 

Let's try an example question.

 

 

Example

Two of the angles in a triangle are 35º and 110º.  Which type of triangle is it?

 

Answer

We must first work out the third angle which will be:

180º - (35º + 110º) = 180º - 145º = 35º

 

So the triangle has angles 35º, 110º, 35º 

Two angles are equal, so it is isosceles.

 

Are you ready to have a go at this now?

 

If you want to look at this introduction again during the activity, just click on the red help button that will appear on the screen.