# Polygons 1

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## Polygons 1

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 180^{0}.

* Equilateral* - All 3 sides equal and all 3 angles equal (to 60

^{0}).

* 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 90

^{0}).

* Right-angled* - One angle is 90

^{0}.

* Obtuse-angled* - One angle is obtuse (greater than 90

^{0}).

The area of a triangle is

However, you must use the **perpendicular **height. That means at 90^{0} to the base.