Quadrilateral in which measure of each angle is less than `180^(@)` is a
(i) Concave quadrilateral
(ii) Convex quadrilateral
(iii) Both

Explain why a rectangle is a convex quadrilateral.

How many diagonals does each of the following have ? A concave quadrilateral.

Which type of angle has measure greater than 180^@ but less than 360^@ ?

What is the sum of the measures of the angles of a convex quadrilateral? Will this property hold if the quadrilateral is not convex? (Make a non-convex quadrilateral and try!)

Given statement below. Identify the statement given below as contrapositive or converse of each other. If a quadrilateral is a parallelogram, then its diagonals bisect each other. (i) If the diagonals of a quadrilateral do not bisect each other, then the quadrilateral is not a parallelogram. (ii) If the diagonals of a quadrilateral bisect each other, then it is a parallelogram.