A polygon is simply a closed 2-dimensional shape made up of straight lines. The word itself actually means 'many-sided shape'.

Obviously, the polygon with the least number of sides is the triangle.

Here are the names of all the polygons with up to 12 sides:

Triangles can be classified using their sides or their angles.

The angles in a triangle always add up to 180⁰.

Equilateral - All 3 sides equal and all 3 angles equal (to 60⁰).

Isosceles - Two sides the same and the angles at the bottom of those sides are equal.

Scalene - No sides or angles equal.

You can also classify triangles by their angles :

Acute-angled - All angles are acute (less than 90⁰).

Right-angled - One angle is 90⁰.

Obtuse-angled - One angle is obtuse (greater than 90⁰).

The area of a triangle is

However, you must use the perpendicular height. That means at 90⁰ to the base.