In: Math
The formula for the amount A in an investment account with a nominal interest rate r at any time t is given by A(t) = a(e)rt, where a is the amount of principal initially deposited into an account that compounds continuously. Prove that the percentage of interest earned to principal at any time t can be calculated with the formula I(t) = ert − 1.
Consider the formula for nominal interest as following:
A(t) = a(e)rt
The annual percentage is determined using the formula:
I(t) = ert - 1
Simplify the above equation as follows:
I(t) + 1 = ert – 1 + 1
I(t) + 1 = ert
Now take natural log on both sides of the above equation,
ln{I(t) + 1} = ln(ert)
rt = ln{I(t) + 1}
r = ln{I(t) + 1}/t
Therefore, the percentage of interest is:
r = ln{I(t) + 1}/t.
Therefore, the percentage of interest is:
r = ln{I(t) + 1}/t.