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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
Moderator
Registered: 2010-06-20
Posts: 6,536

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: 15,673

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
Moderator
Registered: 2010-06-20
Posts: 6,536

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: 15,673

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: 6,536

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: 15,673

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: 6,536

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: 15,673

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: 6,536

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: 90,797

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.

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

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,673

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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