[Music] welcome to math with mr j [Music] in this video i'm going to go through what makes a polygon a polygon so basically what is a polygon and it's a plain closed figure made of line segments so we're going to break that definition down and make it a little easier and simpler now when it comes to polygons there's a checklist and a polygon has to have a check next to each of these three characteristics so we're going to go through what those three characteristics are but before i start that when it comes to polygons they have specific names so for example a three-sided polygon is a triangle a four-sided polygon would be a quadrilateral i'm going to go through those specific names in another video i dropped that link down in the description so let's get back to what makes a polygon a polygon so the first characteristic or thing in our checklist a plain figure or plane shape that just means the figure or shape has to be flat so if it's three dimensional like a cube a pyramid a rectangular prism those are not polygons so again has to be flat next closed so a closed figure or shape and that's exactly what it sounds like it has to be closed so i will give you a counter example that's not a polygon so let's say we almost have a rectangle here but we have this opening that would not be a polygon because it's not closed so not a polygon and then lastly made of line segments so i'll put line segments here this means that there cannot be any rounded edges so for example actually a counter example a circle is not a polygon yes it's flat yes it's closed but it's not made of line segments a polygon has to have a check next to each of these three things so not a polygon another counter example would be a figure like this it's looking like it will be a rectangle but we have a rounded top here so not a polygon because it's not made of all line segments so let's take a look at the right hand side of your screen here we're going to go through five different figures and determine if they are polygons so the first one here this rectangle it's flat it's closed and it's made of line segments so it is a polygon let's go over to the cube here it is not flat it is closed and it is made of line segments but remember we have to have a check mark next to all three characteristics so a cube is not a polygon because it's three dimensional we'll move down to this shape here and we have an opening so that figure is not closed so it is not a polygon over to the oval here it's flat it's closed but it's not made of line segments so it is not a polygon and then lastly the unique shape down there at the bottom it's flat it's closed and it is made of line segments so it is a polygon so there you have it there's what makes a polygon a polygon hopefully that helped thanks so much for watching until next time peace