Prove that in any quadrilateral, the sum of the external angles at two vertices is equal to the sum of the internal angles at the other two vertices.

Prove that in any quadrilateral, the sum of the external angles at two

1.	Prove that in any quadrilateral, the sum of the external angles at two vertices is equal to the sum of the internal angles at the other two vertices.
Answer» Prove that in any quadrilateral, the sum of the external angles at two vertices is equal to the sum of the internal angles at the other two vertices.