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## #1 2014-02-08 18:12:03

niharika_kumar
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### trigonometry#5

A vertical tower stands on a horizontal plane and is surmounted by a flagstaff of height 7 m. At a point on the plane, the angle of elevation of the bottom of the flagstaff is 36° and that of the top of the flagstaff is 45° .Find the height of the tower.

P.S:-I constructed a diagram but I am not able to deal with 36° without using trigonometric table. Pls. help.

*You are never as good as people tell you when you win and you are never as bad as they tell you when you lose.

*Everything happens for a reason,even if we are not wise enough to see them....oprah winfrey

## #2 2014-02-08 19:33:13

Agnishom
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### Re: trigonometry#5

I think using a table is okay in this case

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'The whole person changes, why can't a habit?' -Alokananda

## #3 2014-02-08 22:00:03

bobbym

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### Re: trigonometry#5

Hi;

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #4 2014-02-08 22:44:18

bob bundy
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### Re: trigonometry#5

hi Niharika,

I'm sure tables (or maybe a calculator) is acceptable here.  Trying to get a value for tan 36 without,  is going to be a tough one.

Bob

You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

Nehushtan
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## #6 2014-02-09 00:32:03

Agnishom
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### Re: trigonometry#5

We can do the nested use of this formula

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'The whole person changes, why can't a habit?' -Alokananda

## #7 2014-02-09 00:59:58

gAr
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### Re: trigonometry#5

Hi niharika_kumar,

Perhaps the simplest method is to use De Moivre's formula, taking x= pi/5

Expand LHS and equate the imaginary parts

We can then easily solve it as a quadratic, putting y=sin(x)^2:

Hence,

and

and

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

## #8 2014-02-09 01:07:57

bobbym

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### Re: trigonometry#5

Hi;

The polynomial for cos(x/5) has a neat factorization so it is very easy.

In mathematics, you don't understand things. You just get used to them.
Some cause happiness wherever they go; others, whenever they go.
If you can not overcome with talent...overcome with effort.

## #9 2014-02-09 01:15:00

gAr
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### Re: trigonometry#5

Hi,

Yes, that's also good.

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

## #10 2014-02-12 15:58:55

niharika_kumar
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### Re: trigonometry#5

thanks
got it now.
will do some more study on De Moivre's formula.

*You are never as good as people tell you when you win and you are never as bad as they tell you when you lose.

*Everything happens for a reason,even if we are not wise enough to see them....oprah winfrey

## #11 2014-02-12 16:25:02

gAr
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### Re: trigonometry#5

You're welcome.

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense"  - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."