The angles in a triangle add up to 180º.

This is no different when the angles are algebraic expressions.

**Example**

Form an equation from the angles shown in this triangle and solve it to find the value of a.

**Answer**

The sum of the angles = 180

a + 10 + a - 37 + a = 180

We simplify and solve this equation as follows:

3a - 27 = 180

3a = 207

a = 207 ÷ 3 = 69

**a = 69**º

From this we can then work out what each angle is:

The top angle is 69º

The angle below that is **a + 10 **= 69 + 10 = 79º

The final angle is** a - 37 **= 69 - 37 = 32º

Finally, add them altogether just to check that they do add up to 180:

69 + 79 + 32 = 180º

Great work! Let's try some questions now.