Some designs look like Christmas trees, and some look like sheets of paper. Some designs look like pennies, and some even look like buildings.
This design looks like a paper napkin folded kitty-cornered. The design is called a triangle. It has three sides. The sides meet and form corners. The corners are called angles. A triangle has three angles. All triangles have three sides and three angles. Tri means three.
This design looks like a sheet of paper. It has four sides. The design is called a rectangle. Red means right. An angle is called a right angle when its sides make a square corner. The four angles of the rectangle are right angles.
This design is a rectangle, too. It has four sides and four corners or angles. But it is a special kind of rectangle called a square. It’s called a square because all four sides are the same length.
This design looks like a penny. The design is called a circle. It has no sides and no corners or angles. It just goes all around and meets itself where it began.
This design looks like a famous building in Washington, D.C. The design has five sides and five corners or angles. It’s called a pentagon. The building in Washington, D.C, is called the Pentagon. Penta means five and gon means angle.
All these designs are as flat as they can be, and they have length and width. We call these flat designs planes.