sum of interior angles of a quadrilateral is 360 degrees
On the screen, we see a quadrilateral ABCD in green color. Observe how the shape and angles of this quadrilateral ABCD change as we move the points A, B, C and D. Sum of the interior angles of this quadrilateral ABCD is equal to the sum of the interior angles of the triangles ABD and BCD.
Questions to think about 1. What is the sum of the angles /BDC+/CBD+/BCD (all are in pink color)? 2. What is the sum of the angles /BDA+/ABD+/BAD(all are in black color)? 3. What is the sum of the angles /ABC+/BCD+/CDA+/DAB?