Trigonometry is the branch of mathematics that deals with the study of relationships between sides and angles of a triangle. It is derived from Greek words, Tri meaning  Three , Gon means Angle and Metron means Measure.
The ratio of lengths of two sides of a right angled triangle is called a Trigonometric Ratio. There are six trigonometric ratios

1. Sine of angle  or in short denoted as sinθ is the ratio of opposite to θ to the hypotenuse.
2. Cosine of angle θ or in short cosθ is the ratio of adjacent to θ to the hypotenuse.
3. Tangent of angle θ or tanθ is the ratio of opposite side to θ to the adjacent side to θ.
4. Cotangent of angle θ or cotθ is the ratio of adjacent side to θ to the opposite side to θ.
5. Secant of angle θ or secθ is the ratio of hypotenuse to the adjacent side to θ.
6. Cosecant of angle θ or cosecθ is the ratio of hypotenuse to the opposite side to θ.

The relationships between the trigonometric ratios are:

1. sinθ = , cosecθ = , sinθ x cosecθ = 1.
2. cosθ = , secθ = , cosθ x secθ = 1.
3. tanθ = , cotθ = , tanθ x cotθ = 1.