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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 22,009

1. Using the formula sin(A-B) = sinAcosB - cosAsinB, find the value of sin 15°.

2. If

, and , prove thatby using the formula

.

3. The measure of angle of depression of the bottom of a building on a level fround from the top of the tower is 60° . How far is the building from the tower?

4. A tower is 100/√3 meters high. Find the angle of elevation if the point of observation is 100 meters away from its foot.

5. As observed from the top of a light house, 100 meters high above sea level, the angle of depression of a ship, sailing directly towards it, changes from 30° to 45° . Determine the distance travelled by the ship during the period of observation.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**vichavicha****Member**- Registered: 2008-12-05
- Posts: 1

Q3. Half the height of the tower.

Q5. 50 meters.

Knowledge is Power !

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 22,009

OOps! I am sorry, I forgot to mention in #3 that the tower is 50 meters high.

Regarding your solution to #5, the solution isn't right.

I shall wait for any other membet to attempt, else I shall post all the solutions (sans diagams )

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**rzaidan****Member**- Registered: 2009-08-13
- Posts: 59

Hi ganesh

(1) sin(15°)=sin(45°-30°)=sin(45°)cos(30°)-cos(45°)sin(30°

=(1/√2)(√3/2)-(1/√2)(½)=(√3-1)/2√2

salam

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**Fruityloop****Member**- Registered: 2009-05-18
- Posts: 135

#3. 28.86751346 meters.

#4. 30°

#5. 73.2050808 meters.

**The eclipses from Algol come further apart in time when the Earth is moving away from Algol and closer together in time when the Earth is moving towards Algol, thereby proving that the speed of light is variable and that Einstein's Special Theory of Relativity is wrong.**

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