Introduction to Trigonometry
As we know, the trigonometry is the branch of Mathematics in which we study about the relationship between angles and its sides. In this chapter, we will discuss about trigonometric ratios which are defined in a right-angled triangle.
Trigonometrical Ratios
In the given triangle ABC, \[\angle B=90{}^\circ \]and let angle C is\[\theta \].
Then the trigonometrical ratios are defined as follows:
- \[\sin \theta =\frac{Perpendicular}{Hypotenuse}=\frac{AB}{AC}\]
- \[\cos \theta =\frac{Base}{Hypotenuse}=\frac{BC}{AC}\]
- \[\tan \theta =\frac{Perpendicular}{Base}=\frac{AB}{BC}\]
- \[\cot \theta =\frac{Base}{Perpendicular}=\frac{BC}{AB}\]
- \[\sec \theta =\frac{Hypotenuse}{Base}=\frac{AC}{BC}\]
- \[cosec\theta =\frac{Hypotenuse}{\operatorname{Perpendicular}}=\frac{AC}{AB}\]
Relationship between T-ratios
\[\sin \theta =\frac{1}{\operatorname{cosec}\theta },\,\,\cos \theta =\frac{1}{\sec \theta }\,\,and\,\,\cot \theta =\frac{1}{\tan \theta }\]
From the above, we conclude that sine of an angle is reciprocal to the cosec of that angle and so on.
Tringonometric Ratios of Complementary Angles