The basic elements of any triangle are its sides and angles. Triangles are classified depending on relative sizes of their elements.

 

As regard their sides, triangles may be:

·         Scalene - all sides are different

·         Isosceles - two sides are equal

·         Equilateral -all three sides are equal

 

As regard their angles, triangles may be

·         Acute - all angles are acute

·         Right - one angle is right

·         Obtuse - one angle is obtuse

·         Equiangular - all angles are equal

 

Area of a triangle:

 

 

The sum of the 3 angles of a triangle:

 

 

The Pythagorean Theorem:

 

 

 

Please note that the Pythagorean Theorem is only applicable to right triangles!

 

Here are some special Pythagorean triangles that are often used in many math problems:

 

 

There are also some special triangles that are very useful in solving many math problems: