Trigonometry is the combination of three Greek words ‘**Tri** (Three) +**gon** (sides) +** metron** (measure)’

** Trigonometry** is the study of relationship between the sides and the angles of the triangle.

*Key Concepts*

**Pythagoras Theorem**: When any two sides of a right triangle are given, its third side can be obtained by using Pythagoras theorem.

- Angle measured in anticlockwise direction is taken as
**positive angle**& angle measured in clockwise direction is taken as**negative angle**

- The values of the trigonometric ratios of an angle do not vary with the length of the sides of the triangle, if the angles remain the same.

- The value of sin A or cos A never exceeds 1, whereas the value of sec A or cosec A is always greater than 1 or equal to 1

- Each trigonometric ratio is a real number. It has
**no unit**.

- The value of sin A increases from 0 to 1 when A increases from 0 to 90

- The value of cos A decreases from 1 to 0 when A increases from 0 to 90

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**Important Formulae**

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