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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

### 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.

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

### Re: Algebra -Subject

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

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

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

### 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: Harlan's World
Registered: 2011-05-23
Posts: 16,037

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

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## #19 2013-03-09 05:32:45

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

### Re: Algebra -Subject

Hi;

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

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

Al-Allo
Member
Registered: 2012-08-23
Posts: 324

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

### 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.
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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