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#1 2012-11-26 14:40:18

daydoe12
Member
Registered: 2012-11-18
Posts: 8

I cant figure this out PLEASE HELP

Define a bijection between the sets [-2,8] and [3,5]. Prove your function is actually a bijection.

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#2 2012-11-26 21:13:05

bob bundy
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Registered: 2010-06-20
Posts: 6,390

Re: I cant figure this out PLEASE HELP

hi daydoe12

Welcome to the forum.

How about

Bob


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

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#3 2012-11-27 02:18:38

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,522

Re: I cant figure this out PLEASE HELP

Hi daydoe12

Last edited by anonimnystefy (2012-11-27 02:20:37)


“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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#4 2012-11-27 07:43:44

bob bundy
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Registered: 2010-06-20
Posts: 6,390

Re: I cant figure this out PLEASE HELP

Good answer, Stefy. 

I think yours is correct and I have misunderstood what is wanted.

I'll leave the post as a reminder to me to read the question!

Bob


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

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#5 2012-11-27 09:08:20

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,522

Re: I cant figure this out PLEASE HELP

Hmmm... I thought there was another reason.


“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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#6 2012-11-27 09:10:52

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,390

Re: I cant figure this out PLEASE HELP

Which was ... ?

Bob


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

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#7 2012-11-27 09:16:14

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,522

Re: I cant figure this out PLEASE HELP

Doesn't matter. I hope we solved the OP's problem.


“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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#8 2012-11-28 16:39:02

daydoe12
Member
Registered: 2012-11-18
Posts: 8

Re: I cant figure this out PLEASE HELP

how did you arrive at that answer

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#9 2012-11-28 19:59:53

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,390

Re: I cant figure this out PLEASE HELP

Stefy just looked for a formula of the form y = mx + c so that when x = -2, then y = 3, and similarly when x = 8, y = 5.

My answer used a similar idea but I think his is the right way.

If you think about the straight line graph this produces, every point between -2 and 8, will map onto every point between 3 and 5

And the mapping is reversible.

To prove it, you'd have to show the mapping is 1:1 in both direcctions, and that a point inside the first interval maps to a point inside the resulting interval.

Bob


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

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#10 2012-11-29 15:30:39

daydoe12
Member
Registered: 2012-11-18
Posts: 8

Re: I cant figure this out PLEASE HELP

anonimnystefyLegendary Memberb how did you arrive at that answer

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#11 2012-11-30 02:48:15

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,522

Re: I cant figure this out PLEASE HELP

Hi daydoe12

Bob explained very well in post #9. I don't think I could any better at explaining it.


“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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#12 2012-11-30 04:45:41

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,390

Re: I cant figure this out PLEASE HELP

Thank you Stefy. 

And there was me, about to award you the "Teacher of the Month Award"  smile

Bob


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

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#13 2012-12-03 15:30:49

daydoe12
Member
Registered: 2012-11-18
Posts: 8

Re: I cant figure this out PLEASE HELP

I have tried finding the form using the y=mx+b formula and i cant figure out how she got x+17/5

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#14 2012-12-03 17:05:51

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,603

Re: I cant figure this out PLEASE HELP

Hi daydoe12;

You have -2 -> 3 and 8 -> 5 so call x=-2 and y =3 in the first equation and x = 8 and y = 5 in the second.

When you solve that you get m = 1/5 and b = 17 / 5. Now plug in to the first equation.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#15 2012-12-03 21:52:11

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,522

Re: I cant figure this out PLEASE HELP

bob bundy wrote:

Thank you Stefy. 

And there was me, about to award you the "Teacher of the Month Award"  smile

Bob

I hope you are kidding.

Hi daydoe12

I'm male, not female...


“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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