<P> In certain contexts all the polygons considered will be regular . In such circumstances it is customary to drop the prefix regular . For instance, all the faces of uniform polyhedra must be regular and the faces will be described simply as triangle, square, pentagon, etc . </P> <P> For a regular convex n - gon, each interior angle has a measure of: </P> <Dl> <Dd> (1 − 2 n) × 180 (\ displaystyle \ left (1 - (\ frac (2) (n)) \ right) \ times 180 \, \, \,) degrees, or equivalently 180 (n − 2) n (\ displaystyle (\ frac (180 (n - 2)) (n))) degrees; </Dd> <Dd> (n − 2) π n (\ displaystyle (\ frac ((n - 2) \ pi) (n))) radians; or </Dd> <Dd> (n − 2) 2 n (\ displaystyle (\ frac ((n - 2)) (2n))) full turns, </Dd> </Dl> <Dd> (1 − 2 n) × 180 (\ displaystyle \ left (1 - (\ frac (2) (n)) \ right) \ times 180 \, \, \,) degrees, or equivalently 180 (n − 2) n (\ displaystyle (\ frac (180 (n - 2)) (n))) degrees; </Dd>

Which of the following is not a polygon