have three sides, therefore they have three angles. Interior angles in a triangle sum to a half turn (180˚). Quadrilaterals close quadrilateralA polygon with four straight sides. have four sides ...

Watch the video below which is all about polygons. Polygons are 2D shapes with 3 or more straight sides. All quadrilaterals are polygons, but there are other types of polygons too. As you can see ...