Find Missing Angles Using Given Rules

In this activity, we are going to be looking at angles in special triangles!

 

We know that:-   

 

 

We can use it to find missing angles in triangles!

 

 

Answer

We know that the sum of the three angles is 180^o

We can say that R = 180 - (25 + 96)

R = 180 - 121

R = 59^o

 

There are two special triangles for us to consider.

 

1) The Equilateral Triangle

 

 

All the sides are the same length.

All the angles are the same.

 

 

2) Isosceles Triangle

 

 

Two of the sides are the same length. 

Two of the angles are the same

 

These facts help us to find missing angles in triangles.

 

Let's have a look at a question.

 

Example

Calculate the size of angle A in the isosceles triangle below.

 

 

 

Answer

As the triangle is isosceles, we know that the two angles at the base are the same.

Therefore, angle A  also = 61^o     

 

Let's try some mixed questions now!