# Trigonometry For Class 10

The word ‘trigonometry’ is derived from the Greek words ‘tri’ (meaning three), ‘gon’ (meaning sides) and ‘metron’ (meaning measure). Trigonometry is the study of relationships between the sides and angles of a triangle. Earlier this technique was used to find out the distances of the stars and planets from the Earth. In a right right triangle, the ratio of sides can be represented as a trigonometric angles. We will calculate the ratio of some standard angles and establish identities involving these ratios, known as trigonometric identities.

Trigonometric Ratios-

In a right triangle ABC, right-angled at B, Side AB is called as base(B), BC is called as Perpendicular(P) and side AC is called as Hypotenuse(H).

The trigonometric ratios of angle A in a right triangle ABC are defined as follows-

$\sin A = \frac{P}{H} =\frac{BC}{AC}$

$\cos A = \frac{B}{H} =\frac{AB}{AC}$

$\tan A = \frac{P}{B} =\frac{BC}{AB}$

$\cot A = \frac{B}{P} =\frac{AB}{BC}$

$\sec A = \frac{H}{B} =\frac{AC}{AB}$

$cosec A = \frac{H}{P} =\frac{AC}{BC}$<

It is important to remember some of the standard value of the trigonometric angles. Trigonometric table is helpful in determining the value of various other result.

#### Practise This Question

If Δ ABC and Δ DEF are similar such that 2AB = DE and BC = 8 cm, then Find EF.