It is called a triangle. “Tri” means “three.”
What other triangles do you see.
Triangles are sometimes called trigons.
A triangle is a plane figure having three sides.
How many sides has the plane figure marked B? How many angles?
It is called a quadrangle, or quadrilateral. “Quad” denotes “four.”
What other quadrangles do you see?
Why is Fig. B a quadrangle?
A quadrangle is a plane figure having four sides.
How many sides has the Fig. C?