# Logarithms help

• April 29th 2008, 10:48 AM
av8or91
Logarithms help
If \$2000 is invested at a rate of 12 percent per year, what is the principle after 5 years if the interest is compound quarterly? What is the principle afetr 5 years if the interest is compound quarterly?

Thanks to anyone who can solve.
• April 29th 2008, 10:57 AM
james_bond
Is it $2000\cdot 1.03^{20}=3612.22$? (There are $5*4=20$ "compounds" with $12/4=3 \%$.)
I'm not sure as there are no logarithms in it...
• April 29th 2008, 12:40 PM
av8or91
Doesnt the compund interest formula contain logarithms?
• April 29th 2008, 12:43 PM
icemanfan
Quote:

Originally Posted by av8or91
Doesnt the compund interest formula contain logarithms?

The formula is $A = P(1 + \frac{r}{t})^{nt}$ where r is the annual rate, t is the number of periods per year, n is the number of years, and P is the principal. So there are no logarithms in the formula.
• April 30th 2008, 11:27 AM
av8or91

I have one logarithm problem I cant figure out

Log2x^3= Log2(6-x)
• April 30th 2008, 12:01 PM
topsquark
Quote:

Originally Posted by av8or91

I have one logarithm problem I cant figure out

Log2x^3= Log2(6-x)

New questions go in new threads.

$log_2(x^3) = log_2(6 - x)$

$x^3 = 6 - x$

$x^3 + x - 6 = 0$

There are no "nice" solutions to this equation, so it isn't surprising that you haven't been able to solve it. Numerically I get x = 1.634365293.

-Dan