Question

The sum of the measures of the interior angles of a polygon is 1440 How many sides does it have ________ sides

Answer 1

The only shape that has that much is a decagon 10 sides. the sum of the interior angles of a  Regular Decagon is 1440 degrees. 

Answer 2

To do this sum and to understand angles in polygons let's start at a triangle this has 180 deg,a square has 360 deg,a pentagon has 540 deg. Every time we add a side we add 180 deg. This finally accumulates to 1440 on a ten sided figure.