Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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 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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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 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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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 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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

! BYe

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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)*

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,797

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.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

Hi;

That is not correct. What was your first step?

**In mathematics, you don't understand things. You just get used to them.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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)*

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 298

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 91,693

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

**In mathematics, you don't understand things. You just get used to them.**

Offline