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#1 2014-02-10 15:59:55

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 23,797
Website

Identity?

Given that

is an algebraic identity, what is the value of a-b?

'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.

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#2 2014-02-10 17:50:59

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

Re: Identity?

Hi Agnishom

I'd say it's

.

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.

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#3 2014-02-11 00:23:00

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 23,797
Website

Re: Identity?

What on earth does the question mean?

'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.

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#4 2014-02-11 00:33:09

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,371

Re: Identity?

For what values of a and b is that expression always true.

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.

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#5 2014-02-11 00:44:08

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 23,797
Website

Re: Identity?

How do you do that? (by hand)

'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.

Online

#6 2014-02-11 00:52:18

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,371

Re: Identity?

First I would compute it to give me some insight.

After that, I would substitute x = 0 and x = 1 into that identity and solve for a and b simultaneously.

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.

Online

#7 2014-02-11 01:32:13

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 23,797
Website

Re: Identity?

Where do you get 0 and 1 from? Or are they just arbitary?

'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.

Online

#8 2014-02-11 01:36:11

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,371

Re: Identity?

It is standard when you want to eliminate a parameter that does not count to just plug in any numbers. At the AOPS they go ape at this concept of guessing. We say, they know nothing. It is a little bit of an Ansatz!

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.

Online

#9 2014-02-11 01:40:18

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

Re: Identity?

Equate the coefficients of x:

"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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#10 2014-02-11 01:55:09

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,371

Re: Identity?

Hi gAr;

Yes, that is another way.

Hi Agnishom;

You do it with your package like this:

``````Solve[{a*x + 25 - 5 (x - b) == 0 /. x -> 1,
a*x + 25 - 5 (x - b) == 0 /. x -> 0}, {a, 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.

Online

#11 2014-02-11 02:16:11

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 23,797
Website

Re: Identity?

no attacking other people please. What is the AOPS way?

'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.

Online

#12 2014-02-11 02:17:38

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,371

Re: Identity?

It is a long story and perhaps sometime in the future we will talk about it. For the now, do you understand how to do this?

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.

Online

#13 2014-02-11 02:24:56

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 23,797
Website

Re: Identity?

Yes, thank you all.

If you would tell me the AOPS method, I'd learn another one.

'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.

Online

#14 2014-02-11 02:29:55

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,371

Re: Identity?

Sorry, I did not learn any of their methods. Reppie mathematics makes me nauseous.

If you want a recommendation you should learn all of them but gAr's you should learn first.

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.

Online

#15 2014-02-11 02:39:54

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 23,797
Website

Re: Identity?

OK thank you. What is their method, anyway?

'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.

Online

#16 2014-02-11 02:54:21

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 104,371

Re: Identity?

They never did show me any of their mighty methods, they just kept on saying how mine were bad. This always confused me, X has no answer to a question but says and thinks Y's method which got the right answer is stupid?! Reppie reasoning makes me nauseous.

You have 3 ways there, learn them.

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.

Online