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:

Example

Two of the angles in a triangle are 34º and 112º.  Which type of triangle is it?

Answer

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

180º - (34º + 112º) = 180º - 146º = 34º

So the triangle has angles 34º, 112º, 34º 

Two angles are equal so it is isosceles.

Now, let's put these rules into practice.