Introduction to Trigonometry

The word ‘trigonometry’ is derived from the Greek words ‘tri’ (meaning three), ‘gon’ (meaning sides) and ‘metron’ (meaning measure). In fact, trigonometry is the study of relationships between the sides and angles of a triangle.

Trigonometric ratios of the angle

some ratios of the sides of a right triangle with respect to its acute angles, called trigonometric ratios of the angle.

Trigonometric identities

Trigonometric ratios for some specific angles and establish some identities involving these ratios, called trigonometric identities.


The values of the trigonometric ratios of an angle do not vary with the lengths of the sides of the triangle, if the angle remains the same.


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