# How to calculate the angles of a triangle

All **triangles have three angles** . If the angles have the same size they will measure all 60 degrees and it will be an equilateral triangle, while a right triangle has an angle of 90 degrees that forms an "L". An **angle size** can be **calculated** by measuring the other two angles. Keep reading this article and you will discover **how to calculate the angles of a triangle.**

#### one

One of the options you can find is to **know two angles of the triangle** and have to find the measure of the third angle. Let's take an example: two of the angles of a triangle could be 55 degrees and 25 degrees.

#### two

In this way, to be able to calculate the angles of a triangle you will have to **add the measure of the two angles** that you know. For example, following the case that we have proposed previously, we would have to do this operation:

- 55 + 25 = 80 degrees, the total of the two angles measured

#### 3

Now you must subtract the total sum of the two known angles to 180 degrees. Following the previous example, the operation to be performed would be the following: 180-80 = 100 degrees.

In this way, we find as a result that 100º is the measure of the third angle that was the **unknown angle.**

#### 4

So that you can understand perfectly how to calculate the angle of a triangle, we will give you another example:

If **we know the two angles of a triangle** like the one in the image that are 125 and 30 degrees, to find the third angle of the triangle we have to add the known values:

125 + 30 = 155

And then subtract the previous result to 180; therefore the third angle is:

180-155 = 25 degrees

#### 5

In case it is an **isosceles triangle**, that is, with two sides and equal angles and the third different one, you can find yourself in two situations:

- If you only know the different angle, you will have to subtract the measure of this angle at 180º and then divide it by two. For example: 180º - 40º = 140º and 140º / 2 = 70º so that both equal angles measure 70º
- If you know the size of the equal angles, you must add them and subtract that amount to 180º. Example: 35º + 35º = 70º and 180º - 70º = 110º so that the third angle will measure 110º.

#### 6

These other articles of:

- How to measure the angles of the triangles
- How to calculate the center of a triangle

- The total measure of the three angles of a triangle equals 180 degrees.