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#26 2014-06-03 03:32:56

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 18,205
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Re: Trig Proof Help

Thanks.

Explain the second line please?


'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'
'You have made another human being happy. There is no greater accomplishment.' -bobbym

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#27 2014-06-03 05:00:54

anonimnystefy
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From: The Foundation
Registered: 2011-05-23
Posts: 15,609

Re: Trig Proof Help

Well, you get the middle term from the two middle terms of the previous line and the last term from the last term of the previous line.

Last edited by anonimnystefy (2014-06-03 05:52:23)


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#28 2014-06-03 06:41:26

gAr
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Registered: 2011-01-09
Posts: 3,479

Re: Trig Proof Help


"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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#29 2014-06-12 19:16:36

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 18,205
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Re: Trig Proof Help

Help me!

Evaluate


'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'
'You have made another human being happy. There is no greater accomplishment.' -bobbym

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#30 2014-06-12 19:41:23

bob bundy
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Registered: 2010-06-20
Posts: 6,471

Re: Trig Proof Help

hi Agnishom,

You'll need a large sheet of paper or to write small.  smile

Once you've multiplied this out, nearly everything cancels. 

I converted all to sines with

But you can also simplify with the double angles instead.

Bob

Last edited by bob bundy (2014-06-12 19:44:27)


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

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#31 2014-06-12 19:43:17

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 18,205
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Re: Trig Proof Help

Regarding writing small:
margin.png


'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'
'You have made another human being happy. There is no greater accomplishment.' -bobbym

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#32 2014-06-12 19:45:15

bob bundy
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Registered: 2010-06-20
Posts: 6,471

Re: Trig Proof Help

roflol

Bob


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

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#33 2014-06-12 21:52:31

bob bundy
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Registered: 2010-06-20
Posts: 6,471

Re: Trig Proof Help

But .....

Thought I'd made a mistake as my final simplified answer was a trig function of A, not a number.

Couldn't find a mistake so I set up the expression in Excel and tried a few angles.  I consistently got the result I'd got by algebra and trig formulas.

Bob


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

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#34 2014-06-12 23:38:17

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 18,205
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Re: Trig Proof Help

What results are you getting?

That multiplication is tedious, I've not done it.(yet)

Last edited by Agnishom (2014-06-12 23:38:37)


'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'
'You have made another human being happy. There is no greater accomplishment.' -bobbym

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#35 2014-06-13 00:42:27

bob bundy
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Registered: 2010-06-20
Posts: 6,471

Re: Trig Proof Help

Tedious maybe, but good for you anyway.

I've ended up with cos(2A)

Bob


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

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#36 2014-06-13 03:02:44

ShivamS
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Registered: 2011-02-07
Posts: 3,612

Re: Trig Proof Help

Agnishom, it would have been much simpler if I have seen cos(2A+2B) at the end instead...

I am getting cos(2A).

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#37 2014-06-13 05:40:44

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 18,205
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Re: Trig Proof Help

I am sorry, things are not cancelling.


'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'
'You have made another human being happy. There is no greater accomplishment.' -bobbym

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#38 2014-06-13 05:52:38

ShivamS
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Registered: 2011-02-07
Posts: 3,612

Re: Trig Proof Help

Use a CAS to multiply it out.

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#39 2014-06-13 05:55:37

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 18,205
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Re: Trig Proof Help

There will be no CAS when I will show this to Amrita


'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'
'You have made another human being happy. There is no greater accomplishment.' -bobbym

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#40 2014-06-13 06:09:28

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 89,124

Re: Trig Proof Help

Hi Agnishom;

Just to show you it is possible

TrigReduce[2 Sin[B]^2 + 4 (Cos[B] Cos[B] - Sin[A] Sin[B])*Sin[A] Sin[B] + (Cos[A]^2 - Sin[A]^2) (Cos[B]^2 - Sin[B]^2) -  2 Sin[A] Cos[B]*2 Sin[B] Cos[B]]

In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#41 2014-06-13 06:09:42

ShivamS
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Registered: 2011-02-07
Posts: 3,612

Re: Trig Proof Help

Then you will have to multiply by hand - error prone.

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#42 2014-06-13 07:43:57

bob bundy
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Registered: 2010-06-20
Posts: 6,471

Re: Trig Proof Help

It took me five lines on a sheet of A4 paper.  Admittedly, the lines were quite long, but two long terms cancelled straight away, so that made it simpler.  I'd show you but then you wouldn't get the benefit of doing it yourself smile .

Is this what the computer-wise generation has come to; that we cannot multiply out a simple expression ?

Go to it, boy wonder!

Bob


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

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#43 2014-06-13 07:52:49

ShivamS
Member
Registered: 2011-02-07
Posts: 3,612

Re: Trig Proof Help

bob bundy wrote:

Is this what the computer-wise generation has come to; that we cannot multiply out a simple expression ?

Go to it, boy wonder!

Bob

We're lazy.

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#44 2014-06-13 08:00:43

bob bundy
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Registered: 2010-06-20
Posts: 6,471

Re: Trig Proof Help

But it's good for the brain. 

Bob


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

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