Why do angles in a triangle add to 180?

We know that angles on a straight line add to 180 degrees. Now imagine you have a triangle and the angles are called A, B and C. 

We can orientate the triangles so that we form a straight line. We can see that A, B and C lie on a straight line, so A+B+C=180. 

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Answered by Aaran K. Maths tutor

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