Cant get to grips with re arranging formulae

[chaz699]

Homework Statement

basically i can't get to grips with rearranging formulae

the question is

make U the subject

fv = uv
u+v

(uv is divded by u+v)




2. The attempt at a solution

i try at making them into brackets etc but i can't get to it


can someone show me step by step how to do it


thanks, much appreciated

 

[Hootenanny]

Welcome to Physics Forums.

We won't show you how to do the question, but we will help you do it yourself.

When trying to make something the subject of a formula the best thing to do is to get it out of the fraction. How could you get (u+v) out of the fraction?

 

[chaz699]

erm, put it on the other side of the formula?

 

[Hootenanny]

erm, put it on the other side of the formula?

Sounds good. So what does that give you?

 

[chaz699]

fv(u+v)=uv ?

 

[Hootenanny]

fv(u+v)=uv ?

Looks good. What do you think the next step would be?

 

[chaz699]

erm multiply out the brackets?

 

[Hootenanny]

erm multiply out the brackets?

Sounds good.

 

[chaz699]

so would it befu+fv+vu+v(squared)=uv

 

[Hootenanny]

so would it be


fu+fv+vu+v(squared)=uv

Not quite, note that to expand the bracket you would just multiply everything in the bracket by fv. Do you follow?

 

[chaz699]

i don't quite understand that bit

 

[Hootenanny]

i don't quite understand that bit

Okay what is 2(3+4)?

 

[chaz699]

answer is 14

 

[Hootenanny]

answer is 14

Correct, which is the same as 2x3 + 2x4. Does it make sense now?

 

[chaz699]

er no hah

i don't see how my answer is wrong

 

[chaz699]

would it be FVU+FV(squared) = UV

 

[Hootenanny]

would it be FVU+FV(squared) = UV

Much better .

What do you suppose the next step is?

 

[chaz699]

i actually have no idea

 

[Hootenanny]

i actually have no idea

Try moving all the terms with u in onto the same side.

 

[chaz699]

so then it would be

fv(squared) = uv-fvu?

 

[Hootenanny]

so then it would be

fv(squared) = uv-fvu?

Correct, now what would be the next step?

 

[chaz699]

erm

fv(squared) = u(v-fv)?

 

[Hootenanny]

erm

fv(squared) = u(v-fv)?

Yup.

 

[chaz699]

and then

fv(squared) = u
(v-fv)

 

[Hootenanny]

and then

fv(squared) = u
(v-fv)

Looks good to me

 

[symbolipoint]

chaz699, your notation is a little difficult to follow because, in case you do not yet have a way to use mathematical typesetting, you have also not yet learned how to express things in purely text symbolism. Other than that, you need to practice some number properties operations which lead up to your current exercise. (they are often called, "Field Axioms" or "Properties of Equality". ) Are you by some great chance studying Beginning Algebra or Introductory Algebra? Are you studying Pre-Algebra?

 

[Redbelly98]

That answer is correct, though the left hand side could be simplified further if you wanted to.

 

[chaz699]

im studying a level physics (after high school, before university)

i just find rearranging formula hard

 

[symbolipoint]

From chaz699,

I am studying a level physics (after high school, before university)

i just find rearranging formula hard

Not sure what that physics course means, but that placement suggests what many might consider to be "introductory physics", requiring basic algebra, ability to use simple Trigonometry, but no use of Calculus; a physics course which does not count toward an engineering or science undergraduate degree. Even so, such an introductory course requires, absolutely requires basic algebra skills, so if you are weak as you seem, you need to thoroughly restudy Introductory and most of Intermediate Algebra BEFORE you study your current apparent Introductory Physics course.

As for typesetting to make your math expressions clearer, one of the Reply To Thread features will give you a set of tools which will let you perform some mathematical typesetting. See the icons above the message field; they give you various symbol control effects. Not all the best typesetting features are available, but you may be able to use TEX or LaTEX, or something.
Superscript: X²
Subscript: X₂