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Proving 180° sum for interior angles of a triangle

1. Create a triangle ABC (non-equilateral, non-isosceles) 2. Find midpoint of AB and label it D 3. Rotate triangle ABC 180° with D as the center 4. Find midpoint of BC and label it E 5. Rotate triangle ABC 180° with E as the center

How can you use this figure to prove that the interior angles of this triangle add up to 180°? Remember to write a clear and detailed explanation.