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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 15,544

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

Offline

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 294

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: 87,247

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

Offline

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