# Properties of a triangle

A triangle is a special figure in geometry. He gave the name of a whole branch of mathematics - trigonometry. Therefore, it is very important to know the basic properties of the triangle.

Any triangle can be represented as a figure in which there are three sides and three angles.

- Opposite the other side, which is smaller, there is necessarily a more acute angle. And vice versa.
- If two or more sides are equal, then the angles lying opposite are also equal. A striking example - an equilateral triangle. In it, not only sides are equal, but also angles.
- A property that makes it possible to find unknown angles and indirectly recognize the length of the sides. All its angles are in total 180 degrees.
- If you extend one of the sides, you can get the so-called external angle, which will be equal to the sum of the other two (opposite) angles of the triangle.
- None of the sides of the triangle can beequal to or more than two of its other parties in the amount. If we take one side from the other (greater), then their difference will always be less than the length of the third side.

All these properties apply to any triangle.