Trigonometric Functions

In order to understand trigonometric functions, we can consider the right triangle with an angle θ and the corresponding sides as shown below. The opposite side is the side in front of the angle being observed; the adjacent side is the side touching the vertex where the angle being observed is located; and the hypotenuse is the longest side of the triangle.

For simplicity, we will use the first letter of each side to show the trigonometric functions. The basic trigonometric are cosine, sine and tangent along with their respective reciprocals secant, cosecant and cotangent. These are defined below.

As stated previously, secant, cosecant and cotangent are the reciprocals of cosine, sine and tangent, respectively. Therefore, they can also be written as:

Now that we are familiar with the basic trigonometric functions, we can proceed to analyze right triangles and other type of triangles as we will learn in the future.