Inverse Function

[damo12]

Dear Forum,

Just wondering if someone can provide me with a solution to the following problem:

Inverse(50/20) =

I am looking for a worked through solution to this problem, so that I can solve it manually (i.e. without having to use a calculator). Your help in this matter is much appreciated.

Thank you,
damo12.

 

[Harry_the_cat]

Not really sure what you are asking? There is more than one type of inverse. Can you give the original wording of the question please?

 

[damo12]

Dear Harry_the_cat,

Thank you for your prompt reply. It is much appreciated. I am trying to solve n = ln(FV / PV) / ln(1 + r) to find the number of periods an investment is compounded for. I hope this is helpful.

Thanks,
damo12

 

[Harry_the_cat]

Are you given values for FV, PV and r?

I'm not sure why you are asking about inverse functions?? "ln" stands for natural logarithm, nothing to do with inverse??

 

[JeffM]

$$F = P(1 + r)^n, \ r > - 1, \text { and } P > 0 \implies \\ (1 + r)^n = \dfrac{F}{P} \implies \\ \log\{(1+r)^n\} = \log \left ( \dfrac{F}{P} \right ) \implies\\ n* \log(1 + r) = \log(F) - \log(P) \implies \\ n = \dfrac{\log(F) - \log(P)}{\log(1 + r)}.$$
This has nothing to do with inverses. As a formula, it requires THREE independent variables rather than TWO, namely F, P, and r. Therefore, we cannot possibly help you find the answer because you have given us incomplete information.

You can use natural logarithms, but any logarithm will do. Few problems involving the application of logarithms can be solved without the use of either a log table or a calculator. Virtually all business calculators have a log feature.

Finally, one of our RULES is that you give the original problem completely and exactly so we can see whence you are coming and whither you need to go. Another of our RULES is that you show what work you were able to do on your own so we know where to start giving you help. In my opinion, your original post is one of the worst I have ever seen on this site. We want to help you, but you need to follow the rules explained in READ BEFORE POSTING.

 

[damo12]

$$F = P(1 + r)^n, \ r > - 1, \text { and } P > 0 \implies \\ (1 + r)^n = \dfrac{F}{P} \implies \\ \log\{(1+r)^n\} = \log \left ( \dfrac{F}{P} \right ) \implies\\ n* \log(1 + r) = \log(F) - \log(P) \implies \\ n = \dfrac{\log(F) - \log(P)}{\log(1 + r)}.$$
This has nothing to do with inverses. As a formula, it requires THREE independent variables rather than TWO, namely F, P, and r. Therefore, we cannot possibly help you find the answer because you have given us incomplete information.

You can use natural logarithms, but any logarithm will do. Few problems involving the application of logarithms can be solved without the use of either a log table or a calculator. Virtually all business calculators have a log feature.

Finally, one of our RULES is that you give the original problem completely and exactly so we can see whence you are coming and whither you need to go. Another of our RULES is that you show what work you were able to do on your own so we know where to start giving you help. In my opinion, your original post is one of the worst I have ever seen on this site. We want to help you, but you need to follow the rules explained in READ BEFORE POSTING.

Dear JeffM,

Thank you for your prompt and detailed response. It is very much appreciated. I apologise for not reading the forum rules before posting. I will do better next time.

Thank you,
damo12.