Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

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'

I'm not crazy, my mother had me tested.

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,015

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

The knowledge of some things as a function of age is a delta function.

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'

I'm not crazy, my mother had me tested.

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

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)*

Children are not defined by school ...........The Fonz

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'

I'm not crazy, my mother had me tested.

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

Bob

Children are not defined by school ...........The Fonz

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: 7,577

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

Children are not defined by school ...........The Fonz

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'

I'm not crazy, my mother had me tested.

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

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

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,648

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'

I'm not crazy, my mother had me tested.

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,648

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'

I'm not crazy, my mother had me tested.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 104,288

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.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,648

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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

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

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

Offline

**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,648

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: 7,577

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

Offline