1. ## rearranging fomulae help

dont have a clue how to do this. can someone show me as well as the steps if u have the time with the answer.
these are some questions we got during class(make x the subject).. sry dont know to get squared and cubed signs on here.

sry pretty long post

1. y= ax+ bx

2. y= 3x/m +2x

3. y=mx(squared)-a/b

4. y= 1/3 mx(cubed)

5. y= x/y + y/2

6. y= 1/2 mx+ kx

7. m(x-y)=3 (2x-7)

8. y=mx-abx/3

9. y= 4/x + c

10. y= x+a/x+b

2. Originally Posted by maths noob

1. y= ax+ bx
$y=ax+bx \Rightarrow y=(a+b)x \Rightarrow x=\frac{y}{a+b}$

You want something like this to do?

3. yes

4. Originally Posted by maths noob
3. y=mx(squared)-a/b
$y = mx^2 - \frac{a}{b}$

(I assume $m$, $a$ and $b$ are all constants)

Add $\frac{a}{b}$ to both sides:

$y + \frac{a}{b} = mx^2$

Divide both sides by $m$:

$\frac{y}{m}+\frac{a}{bm}$

Take the square root of both sides - not forgetting the $\pm$ sign:

$x = \pm \sqrt{\frac{y}{m}+\frac{a}{bm}}$

Can you try one now?

5. i actually just got help off someone so i can do 1,2,3,5 type questions now

would no.9 be

y=4/x=c

y= 4+cx

y+4/c=x???

anyways could you post how to do and answers to 4,6-10 just so i can get a better feel then having a go afterwards

6. Originally Posted by maths noob
4. y= 1/3 mx(cubed)

6. y= 1/2 mx+ kx

7. m(x-y)=3 (2x-7)

8. y=mx-abx/3

9. y= 4/x + c

10. y= x+a/x+b

anyways could you post how to do and answers to 4,6-10 just so i can get a better feel then having a go afterwards
I'll post the answers because I don't want my working copied verbatim

4. $\sqrt[3]{\frac{3y}{m}}$

6. $x = \frac{y}{0.5m+k} = \frac{2y}{m+2k}$

7. $x = \frac{my-21}{m-6} = \frac{21-my}{6-m}$

8. $x = \frac{3x}{3m-ab} = \frac{x}{m-\frac{1}{3}ab}$

9. $x = \frac{4}{y-c}$

10. $x = \frac{a-yb}{y-1}$

7. but how am i meant to know how to do them to get to the answer?

8. Originally Posted by maths noob
i actually just got help off someone so i can do 1,2,3,5 type questions now

would no.9 be

y=4/x=c

y= 4+cx

y+4/c=x???

anyways could you post how to do and answers to 4,6-10 just so i can get a better feel then having a go afterwards
Nope.

$y = 4/x + c$

Multiply it all by x:

$xy = 4 + cx$

Gather all the x's on one side:

$xy - cx = 4$

Get x in one place:

$x (y-c) = 4$ (this is an example of use of the distributive law)

$x = \frac 4 {y-c}$

9. Originally Posted by maths noob
but how am i meant to know how to do them to get to the answer?
Same way as you learn to do anything. Watch what's being done, imitate it, then apply the technique.