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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.


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#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'
'Who are you to judge everything?' -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.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#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.  eek

Bob


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

#5 2014-02-09 00:11:41

Nehushtan
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Re: trigonometry#5


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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'
'Who are you to judge everything?' -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.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#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.


friendship is tan 90.

#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."

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