A triangle is a polygon with three sides. The notation that is generally used is to name its vertices with the capital letters A, B and C (but they can be others, as long as they are uppercase) and sides opposite these vertices are identified with lowercase letters.
A Triangle must meet certain properties to be considered as such. some of them are the following:
- The sum of the interior angles of a triangle is equal to 180 °.
- Each equilateral triangle is equiangular, that is, the measures of its internal angles are equal, in this case each angle measures 60 °
- If two sides of a triangle have the same measure, then the opposite angles are also of equal measure.
- In a triangle, a larger side opposes a larger angle.
- The value of an exterior angle of a triangle is equal to the sum of the two non- adjacent interiors.
- One side of a triangle is smaller than the sum of the other two and greater than their difference. a (b + cab) - c
A triangle widely used in trigonometry is the right triangle, in which the study of the relationship between its sides is done by the Pythagorean theorem.
Pythagoras' theorem: Pythagoras stated the famous theorem that bears his name and that relates the sides of a right triangle. This theorem says:
"The area of the square built on the hypotenuse of a right triangle is equal to the sum of the areas of the squares built on the legs."
Triangles are classified according to two criteria: according to their sides and according to their angles, these can be used together or separately:
1. Classification of triangles according to their sides
- A triangle is equilateral if it has three equal sides.
- A triangle is isosceles if it has two of its equal sides.
- A triangle is scalene if it has three unequal sides.
2. Classification of triangles according to their angles
In this case, we look at the angles to perform the classification. Namely:
- A triangle is acute if it has all its acute angles.
- A triangle is right, if it has one of its right angles, that is, 90º.
- A triangle is obtuse if it has an obtuse angle.
