1. S2B Chapter 11 Introduction to Trigonometric Ratios

2. 2009 Chung Tai Educational Press. All rights reserved. © The term ‘trigonometry’ originated from two Greek words with meaning ‘surveying’ and ‘triangle’. Therefore this knowledge is related to triangle surveying. Trigonometry was first developed by astronomers from Greece, Persia and Arabia in around 200AD. Origin of Trigonometry

3. 2009 Chung Tai Educational Press. All rights reserved. © Origin of Trigonometry Regiomontanus (1436 - 1476), a German mathematician, arranged the knowledge of trigonometry systematically and made it a branch of mathematics.

4. 2009 Chung Tai Educational Press. All rights reserved. © D E Similar Right-angled Triangles When an acute angle is fixed (say 35  ) in a right- angled triangle ABC, the ratios of any two sides in  ABC are the same as the corresponding ratios in a triangle similar to  ABC. A B C i.e.

5. 2009 Chung Tai Educational Press. All rights reserved. © Cosine Ratio of an Angle In any right-angled triangle ABC, the ratio of the adjacent side to the hypotenuse of  B is known as ‘the cosine ratio of  B’, denoted by ‘cos  B’. cos  B  Adjacent side Hypotenuse i.e.

6. 2009 Chung Tai Educational Press. All rights reserved. © Sine Ratio of an Angle In any right-angled triangle ABC, the ratio of the opposite side to the hypotenuse of  B is known as ‘the sine ratio of  B’, denoted by ‘sin  B’. sin  B  Opposite side Hypotenuse i.e.

7. 2009 Chung Tai Educational Press. All rights reserved. © Tangent Ratio of an Angle In any right-angled triangle ABC, the ratio of the opposite side to the adjacent side of  B is known as ‘the tangent ratio of  B’, denoted by ‘tan  B’. tan  B  Opposite side Adjacent side i.e.

8. The End