How to undo exponentiation

D

doraima29

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Oct 19, 2009
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2
Hi,

I was solving for a problem that requires undo an exponentiation for a business math problem.

I solved using the log function on my calculator; however, the final answer coming from an online homework says otherwise.
I know this should be on the business math section; however I want to be clear how to undo an exponentiation. If the exponents are negative.

This is what I am trying to solve:

PMT = FV (1-(1+i)^-n)/i

where: FV = Future value, i= interest rate converted to decimals, n= number of periodic payments.
Find: PMT = payment of first deposit

I changed the formula so I can solve for PMT.

PMT = FV (1-log(n)(1+i))/i

Am I doing anything wrong about undoing the exponentiation for this problem.
 
doraima29 said:
Hi,

I was solving for a problem that requires undo an exponentiation for a business math problem.

I solved using the log function on my calculator; however, the final answer coming from an online homework says otherwise.
I know this should be on the business math section; however I want to be clear how to undo an exponentiation. If the exponents are negative.

This is what I am trying to solve:

PMT = FV (1-(1+i)^-n)/i

where: FV = Future value, i= interest rate converted to decimals, n= number of periodic payments.
Find: PMT = payment of first deposit

I changed the formula so I can solve for PMT.

PMT = FV (1-log(n)(1+i))/i

Am I doing anything wrong about undoing the exponentiation for this problem.
Click to expand...

You CANNOT just use "ln" to undo exponentiation like you tried. At least - you have to use "ln" on both sides.

Why are you trying to do "ln" - since you have to find PMT?

Just use the x[sup:10zk1sr5]y[/sup:10zk1sr5] button in your calculator - properly.
 
You could multiply [1/(1+i)] ---- n times, to calculate (1+i)[sup:2zmty531]-n[/sup:2zmty531]

.
 
doraima29 said:
Hi,

I don't have x^y on my calculator. Is there a similar function?
Click to expand...

It seems odd to have a calculator with exp and ln, but not x^y.

To find x^y, you could do the following steps :

* find ln(x)
* multiply this by y, to get y*ln(x)
* take exp of this, to get exp(y*ln(x)) = x^y
 
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