You are not logged in.

- Topics: Active | Unanswered

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

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,544

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

Offline

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

"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."

Offline

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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,426

hi Agnishom,

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

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

Offline

Regarding writing small:

'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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,426

Bob

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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,426

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

Offline

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)*

'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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,426

Tedious maybe, but good for you anyway.

I've ended up with cos(2A)

Bob

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,555

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

I am getting cos(2A).

Offline

I am sorry, things are not cancelling.

'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

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,555

Use a CAS to multiply it out.

Offline

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

'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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,238

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]]`

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,555

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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,426

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 .

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

Go to it, boy wonder!

Bob

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,555

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.

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,426

But it's good for the brain.

Bob

Offline