Equilateral triangle

An equilateral triangle is a triangular regular polygon. Since all its angles are the same, it is equiangular and it can also be called an regular triangle.

Properties
Its interior angle is 60&deg; which can be found by the formula for interior angles:

$${{(3 - 2)\cdot180^\circ}\over 3}=60^\circ$$.

For side length a,
 * Its area is $$\frac34a^2\cot\frac{\pi}{4}=\frac{\sqrt{3}}{3}a^2\approx 0.433a^2$$
 * Its perimeter is $$3a$$.
 * Its apothem is $$\frac{\sqrt{3}}{6}a$$