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#1 2007-06-05 06:42:54

weirdguy66
Guest

subject of the formula

i have tried this but i just cant see how it can be done

make u the subject of the formula d=ut+kt²

i figured that you could use substitution but i dont know how to go about it.

please help

thanks

#2 2007-06-05 06:45:52

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Re: subject of the formula

I'm pretty sure this is right:

Last edited by Daniel123 (2007-06-05 06:48:02)

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#3 2007-06-05 06:49:53

weirdguy66
Guest

Re: subject of the formula

thanks man, that really helps.

#4 2007-06-05 07:06:20

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Re: subject of the formula

No problem! You just need to remember that when you have a rearranging question that has two terms with the same letter on the same side of the equation, then you factorise, e.g.:

ut + kt² (the common letter is the 't', so you take the 't' out by factorising)
t (u+kt)

then you just need to move the 't' you have taken out to the other side, as well as the kt.

Last edited by Daniel123 (2007-06-05 07:13:24)

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#5 2007-06-05 07:25:07

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

Re: subject of the formula

you could also do it this way: the way i would generally do it:

the only time you need to factorise is when the term you're trying to single out is in more than one term like:


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#6 2007-06-05 07:28:18

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Re: subject of the formula

luca-deltodesco wrote:

the only time you need to factorise is when the term you're trying to single out is in more than one term like:

That's what I attempted to say, but I couldn't put it into words that anyone other than me would understand... smile although I'm not quite A level standard though tongue

Last edited by Daniel123 (2007-06-05 07:28:43)

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#7 2007-06-05 07:52:25

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: subject of the formula

I'd have also solved it luca's way.
Generally, the way to do these is to first put all terms containing the subject on one side and all term that don't on the other, then factorise out the subject and divide through by what you get left.

The only ones that can't be solved like that are those that have different orders of the subject, such as t in the original example. In those cases, completing the square is normally the way to go (or the quadratic equation if you're lazy tongue).


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It wanted to be normal.

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