# Short Notes: Introduction to Trigonometry 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 TheoremWhen 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 to 90 # Important Formulae   