1.Drag points P and Q to the circumference of the circle

- Now measure the sum of angle P and Q ,is it 180? Why the sum of angle P and Q is 18.Hint: use the property of angle subtended by arc of a circle

2.Observe all properties of angles in a circle which are visible here

3.If angle Q is equal to exterior angle P, is it possible that point P is not on the circle? check that remaining points D, B, Q are on the circle or not and why

4.Measure the sum of all the interior and exterior angles , is it 360? Now drag point P or Q outside the circle again check the sum of all the interior and exterior angles

OBSERVATIONS:

-Sum of opposite angles of quadrilateral is 180,then it is cyclic quadrilateral

-if all the points are concyclic quadrilateral is cyclic quadrilateral.

-Sum of all the exterior and interior angle of the every quadrilateral is 360