 Hello and welcome to the session. In this session we discuss the following question which says define a convex quadrilateral and a concave quadrilateral. Let's see the solution now. First of all let's define a convex quadrilateral. This is a quadrilateral in which the measure of each angle is less than 180 degrees. This abcd is a convex quadrilateral since the measure of each angle is less than 180 degrees. Next let's define a concave quadrilateral. This is a quadrilateral in which the measure of at least one of the angles is more than 180 degrees. Here the quadrilateral P2RS is a concave quadrilateral. Its angle S has measured more than 180 degrees. So this completes the session. Hope you have understood the solution of this question.