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

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

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
Registered: 2010-06-20
Posts: 8,354

hi daydoe12

Welcome to the forum.

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

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

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

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

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## #4 2012-11-27 07:43:44

bob bundy
Registered: 2010-06-20
Posts: 8,354

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

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

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

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

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

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## #6 2012-11-27 09:10:52

bob bundy
Registered: 2010-06-20
Posts: 8,354

Which was ... ?

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

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

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

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

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## #8 2012-11-28 16:39:02

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

how did you arrive at that answer

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

bob bundy
Registered: 2010-06-20
Posts: 8,354

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

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

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

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

anonimnystefyLegendary Memberb how did you arrive at that answer

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

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

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

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## #12 2012-11-30 04:45:41

bob bundy
Registered: 2010-06-20
Posts: 8,354

Thank you Stefy.

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

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

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

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

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
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

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.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

bob bundy wrote:

Thank you Stefy.

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

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

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