  # Concise Selina Solutions for Class 9 maths Chapter 22 Trigonometrical Ratios

The ratio between the lengths of a pair of two sides of a right-angled triangle is called a Trigonometrical Ratio. Trigonometry is concerned with the measurement and calculation of the lengths of sides and the sizes of angles of triangles. There are three fundamental ratios called the sine, the cosine and the tangent of the angle. These are abbreviated to sin, cos and tan. It is defined as the values of all trigonometric function based on the value of the ratio of sides in a right-angled triangle. Ratios of sides of a right-angled triangle for any of its acute angles are known as the trigonometric ratios of particular angle. In this chapter, students learn about the topic of Trigonometrical Ratios of a triangle, dealing with the relations of sides and angles of right-angled triangles. The three sides of a right-angled triangle give six trigonometrical ratios; namely sine, cosine, tangent, cotangent, secant, and cosecant.