Tue September 18, 2012 By:

Prove the sum of triangle is 180 degres

Expert Reply
Tue September 18, 2012
Start with the following triangle with arbitrary values for the angles:

Since angle a, angle b, and angle c make a straight line,

angle a + angle b + angle c = 180 degrees

Since alternate interior angles are equal, angle a = angle x and angle b = angle y

Therefore, angle x + angle y + angle c = 180 degrees
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