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 = 69º

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

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