This video is about Trigonometric ratios
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00:00We are going to start unit 6 of the book of Grade 9. This is one of the most important
00:08chapters of this book, Trigonometry and Bearings. What is trigonometry? Trigonometry is basically
00:14the study of triangles in which we consider the sides and angles of a triangle and bearing
00:21is basically the measurement of angle in degrees and we also have to start that measurement
00:26from the north direction. So, basically these are the two topics which are introduced in
00:32unit 6. First of all, before starting unit 6 and especially for the exercise 6.4, your
00:40concept of trigonometric identities should be absolutely clear and you have to remember
00:46them as well. Because if you don't remember them, you won't be able to further solve questions.
00:51We have many types of identities which are introduced in your book. These are reciprocal
00:57identities. You have six functions. Reciprocal identities are basically the inverse of sine
01:10theta and now you have to learn this. Cosecant theta is inverse of sine theta. Secant theta
01:17is inverse of cos theta and cot theta is inverse of tan theta. There are 3 simple reciprocal
01:24identities. Cosecant is inverse of sine, secant is inverse of cos and cot is inverse of tan.
01:33You have to remember them. Why? Because when you are going to solve the questions, it will
01:38be implemented there. You won't be able to solve the questions without memorizing them.
01:43After that, we have quotient identities. Now, what are quotient identities? You have two
01:49quotient identities. Tan theta is equal to sine theta divided by cos theta is equal to
01:59tan theta. This is our first quotient identity. Cot theta is equal to tan and cot. They are
02:08inverse of each other. You have three identities and they are also very important. You won't
02:15be able to solve the questions without memorizing them. These are pi-theta and pi-cos. You have
02:22three identities and they are also very important. You have three identities and they are also
02:32very important. You won't be able to solve the questions without memorizing them. These
02:37are Pythagorean identities. In Pythagorean identities, you have to remember them. Sine
02:44square theta plus cos square theta is equal to 1. Secant square theta minus tan square
02:50theta is equal to 1 and cosecant square theta minus cot square theta is equal to 1. If we
02:57solve the questions without memorizing them, we will be able to solve the questions easily.