# Base concept of Trigonometry and its Derivation

**Topic discussed in this video:**

- Base Concept of Trigonometry and its derivation

One of the beauties of trigonometry is that its rules are equally applicable for all similar triangles because the base concept of trigonometry was derived from the similarity of triangles and in this video, I am going to discuss that base concept with its derivation.

But before I begin our main concept, let’s revise right triangles first.

As we have learned in the right triangles that we have a fixed interior angle of . The side opposite this interior angle is the longest side and it is known as hypotenuse. Because of this fixed interior angle of , the other two interior angles are always complementary. That means,

So, if I assume as q then will always be .

As the trigonometry is about the relationships between the interior angles and the side lengths. So, from now onwards, I am going to assume the interior angle q as my main angle for all the concepts and derivations. Also, AB is going to be the opposite side of my main angle and BC is going to be the adjacent side. These special names for all three sides linked with interior angles are going to be very helpful with our main concept and derivation.

Let’s begin the main concept of trigonometry………