Question

why triangle has 180 degrees

Answer 1

Its a property of a complete triangle that the sum of all the three angles must be 180°.

Hope this helps. Thank you. ☺

Answer 2

As we all know that if we add up the interior and exterior angles of one corner of a triangle, we always get 180°. So the exterior angle is equal to the sum of the other two triangle.

Hope it helps you!!!