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.