# Thread: V=B-q/k In(r-1): Make r the subject.

1. ## V=B-q/k In(r-1): Make r the subject.

hi

i have a equation which i dont know how to solve it, as i have never seen this equation before !!

question

given : V=B-q/k In(r-1)

make r subject of the formula ?

could you please explain what they want exactly

thanks

2. Originally Posted by manfred
hi

i have a equation which i dont know how to solve it, as i have never seen this equation before !!

question

given : V=B-q/k In(r-1)

make r subject of the formula ?

could you please explain what they want exactly

thanks
They want you to solve for r in terms of the other pronumerals. I suggest that you first attempt to make ln(r-1) the subject.

By the way, your expression is ambiguous. Is it meant to be V=B-q/[k In(r-1)] or V=[B-q/k] In(r-1) ....?? Or V=(B-q)/[k In(r-1)] or V=B-(q/[k In(r-1)]) etc. etc. Please use bracketes, or take the couple of minutes to learn how to use latex (click on the appropriate link in my signature).

3. Originally Posted by mr fantastic
They want you to solve for r in terms of the other pronumerals. I suggest that you first attempt to make ln(r-1) the subject.

By the way, your expression is ambiguous. Is it meant to be V=B-q/[k In(r-1)] or V=[B-q/k] In(r-1) ....?? Or V=(B-q)/[k In(r-1)] or V=B-(q/[k In(r-1)]) etc. etc. Please use bracketes, or take the couple of minutes to learn how to use latex (click on the appropriate link in my signature).
yes i meant V=[B-q/k] In(r-1)

could you please show me the solutions to it then i can understand how and where its coming from in solving it please thanks

4. Originally Posted by manfred
yes i meant V=[B-q/k] In(r-1)

could you please show me the solutions to it then i can understand how and where its coming from in solving it please thanks
$\displaystyle V=\left(B - \frac{q}{k}\right) \cdot \ln(r-1)$

$\displaystyle \frac{V}{B - \frac{q}{k}} = \ln(r-1)$

$\displaystyle e^{\frac{V}{B - \frac{q}{k}}} = r - 1
$

$\displaystyle 1 + e^{\frac{V}{B - \frac{q}{k}}} = r$

5. Originally Posted by manfred
hi

i have a equation which i dont know how to solve it, as i have never seen this equation before !!
I hope you do NOT mean that the only equations you can solve are those that you have seen before!

question

given : V=B-q/k In(r-1)

make r subject of the formula ?

could you please explain what they want exactly

thanks
By the way, it is "ln" (small L) NOT "In", for natural logarithm.

6. Originally Posted by manfred
yes i meant V=[B-q/k] In(r-1)
Well, make your life easier by making x = B - q/k; then:
Ln(r - 1) = V / x
r - 1 = e^(V / x)