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#1 2013-03-07 09:14:55

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Algebra -Subject

Hi

s = ut +½at^2

So I want you to tell me why my way of doing is wrong : (a must be the subject)

            -ut        s = ut +½at^2     -ut

            / ½t^2      s-ut=½a^t2  / ½t^2    (This is how I think I should have done it, because we want only the a, so you divide all in one shot)


s-ut/ ½t^2=a  ===> a=s-ut/ ½t^2

I Know this is the wrong answer, but explain me why my way of doing is wrong, because I have no idea why ! Thanks

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#2 2013-03-07 09:27:04

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

Is this the question?

You want to solve for a?


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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#3 2013-03-07 09:29:58

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

I want 'a' to be the subject of the formula, I already did my way of doing, which is wrong, and would like to know wy it's wrong. Thanks

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#4 2013-03-07 09:33:16

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

Just trying to get the exact question. You want a on the left by itself and that is the correct form in post #2.

This is the answer.

Last edited by bobbym (2013-03-07 09:36:09)


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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#5 2013-03-07 09:37:05

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

Yes, that's what I want, 'a' on the left of the formula.

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#6 2013-03-07 09:43:02

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

Times everything by 2

Subtract 2ut from both sides

Divide by t^2.

Clean up.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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#7 2013-03-07 09:47:20

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

Oh wow.....It's clear now ! I understand now ^^  thanks. The way you present the formula is more clean, I got misleaded by my mess lol

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#8 2013-03-07 09:50:06

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

Just remember I treated it algebraically. Like a bunch of letters. t must never be zero.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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#9 2013-03-07 10:08:11

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

Ok, by curiosity, do you know where I could practice more of these ?

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#10 2013-03-07 10:09:14

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

I could give you a few if you want or I will look up a page if there is one.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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#11 2013-03-07 10:13:50

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

That would be great, always looking to practice tongue Anyway, I need to go
!  BYe

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#12 2013-03-07 10:18:17

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Okay, here are three.

Make a the subject.


Or

Make b the subject.

And last!

Make b the subject.

Last edited by bobbym (2013-03-07 10:34:30)


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline

#13 2013-03-08 05:23:16

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

i did the first one

a=s-ut^2

btw, do you have an article on these ? im having a hard time doing these ^^ ty

a(x)a-x/-2=b

b=1/u.a

Last edited by Al-Allo (2013-03-08 05:33:59)

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#14 2013-03-08 13:26:21

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

I made them up for you.

You should get

Last edited by bobbym (2013-03-08 13:26:48)


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline

#15 2013-03-08 16:45:36

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

Oh man, I don't know why but I'm having trouble with these. I dont know where to begin and always get a different answer >.< And what I meant by article is something that tells how to approach rearranging formulas

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#16 2013-03-08 20:09:17

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

Follow along with what I do:

Subtract u from both sides.

Clean the denominator on the right, t*a*t^2 = a*t^3.

Multiply both sides by a

Divide both sides by (s - u)

Last edited by bobbym (2013-03-08 20:22:11)


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline

#17 2013-03-09 05:30:31

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

is the third one a=ub/2 ??? hope i got it

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#18 2013-03-09 05:32:23

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,237

Re: Algebra -Subject

Hi Al-Allo

You should have a on the left hand side. And the expression you got that isn't correct either.


“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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#19 2013-03-09 05:32:45

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

That is not correct. What was your first step?


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline

#20 2013-03-09 05:38:11

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

here is what I did : (like I said, Im not sure how to begin these, to many steps, but the simple ones I can easily do them)

*bu 1/a=1/b+1/u *bu

*a 1/a *bu= 2 *a

bu/2=2a/2

a=bu/2

Last edited by Al-Allo (2013-03-09 05:38:31)

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#21 2013-03-09 05:42:21

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

Okay, let's follow your idea and times both sides by bu.

You should get:

Last edited by bobbym (2013-03-09 05:42:39)


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline

#22 2013-03-09 05:44:39

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

OKay, but isn't it supposed to be 1+1 on the right side ?...

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#23 2013-03-09 05:49:08

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Hi;

No, you are cancelling too much. let's see what happens just on the left.

Now cancel the b in the first fraction.

Are you okay up to here?


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline

#24 2013-03-09 05:51:29

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Algebra -Subject

AHHHHHHHHHH... okay that why. Mh bobbym, could we continue later this way of doing ? Because I need to go like now. We shall continue later, when I'm online ? Thanks for your help

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#25 2013-03-09 05:59:18

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,286

Re: Algebra -Subject

Okay, I will see you later. Have a good day.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline

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