## Tuesday, October 20, 2015

### All Trigonometry Identities(Formula), Concept of Degree Radian Minutes Seconds, Cosine Rule and Sine Rule

In this video first I have explained around 25 trigonometric identities/formulas. These are those formulas which you should memorize by your heart so that it becomes easy for you to recall them when you would be attempting questions in the real exam. These 25 formulas are more than enough to cater to nearly all type of questions that you would encounter in exam. I have orally explained the proving of around half of these formulas and I have explained how many of these formulas are interrelated to each other and memorizing one will automatically reiterate the second.

After the formulas I have once again in very brief explained Cosine Rule and Sine Rule. These two rules I have explained very properly with proof in my geometry videos but for the sake of geometry I just repeated them here.

Then I have solved four typical trigonometry questions that we often see in exams and we also saw them when we were in High School.

Through the fifth question I have tried to explain you the theory of how to convert Degree, Radian, Minutes and Seconds into one another. This type of questions have seldom been asked in competitive exams so I have also covered them here.

The questions discussed in this video are as follows -

Ques 1. From the top of a 200 meter high building, the angle of depression to the bottom of a second building is 45 degrees. From the same point, the angle of elevation to the top of the second building is 30 degrees. Calculate the height of the second building.

Ques 2. The lengths of the side AB and side BC of a scalene triangle ABC are 12 cm and 8 cm respectively. The measure of angle C is 60 degree. Find the length of side AC.

Ques 3. If the shadow of a building increases by 10 meters when the angle of elevation of the sun decreases from 45 degree to 30 degree, what is the height of the building ?

Ques 4. Raman is riding vertically in a hot air balloon, directly over a point P on the ground spots a parked car on the ground at an angle of depression 45 degree. The balloon rises 100 meters. Now the angle of depression of the car is 60 degree. How far is car from point P ?

Ques 5. Convert (102 degree 45 minutes 54 seconds) into decimal/fraction. (The exact sign of minutes and seconds is shown in the video)

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