UNIT 04: TRIANGLES

Definition

A triangle ABC is a flat shape limited by three lines which intersect each other two to two, defining the segments a, b and c, which are the sides of the triangle. In order to get those three segments forming a triangle ABC it is necessary that the length of each of those segments is smaller than the addition of the other two and bigger than their subtraction.
A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments.
The addition of all the internal angles in the triangle is 180º.

How to label a triangle

• The vertices of the triangle are named with capital letters (A, B, C)
• The sides of the triangle are named with the letter of its opposite vertex (a, b, c)
• The angles of the triangle are named with the letter of the vertex and angle symbol (^).

Types of triangles

Triangles are classified two ways:

Due to their SIDES:

Equilateral
Three equal sides and angles.

Isosceles
Two equal sides and angles.

Scalene
No equal sides or angles.

Due to their INTERNAL ANGLES

Acute
All their angles are ACUTE.

Right
One RIGHT ANGLE.

In right triangles, the sides that form the right angle are called LEGS and the side that faces them is called HYPOTENUSE.

Obtuse
One OBTUSE angle.