# Precalc HELP, ASAP. No idea, Please explain

• Jul 28th 2010, 06:49 PM
danielh9103
Precalc HELP, ASAP. No idea, Please explain
Solve leaving answers in terms of e or ln.

a) e^(5x-3)=10

b) 5^(3+x) = 20^x-3
• Jul 28th 2010, 06:56 PM
lvleph
$\displaystyle \ln$ basically undoes $\displaystyle e$. So if you want to isolate the exponent of $\displaystyle e^x$ we can take the natural log like so $\displaystyle \ln e^x = x$. Now don't forget whatever you do to one side of an equation you have to do to the other side of the equation. Also, don't forget that $\displaystyle \ln a^x = x\cdot \ln a$. Make an attempt at these problems and post what you come up with.
• Jul 28th 2010, 07:03 PM
danielh9103
alright thank you!

is this correct:

5x - 3 = ln 10

5x = ln 10 + 3

x = [(ln 10) + 3] / 5
• Jul 28th 2010, 07:05 PM
lvleph
Yep.
• Jul 28th 2010, 07:15 PM
danielh9103
thank you, and for the second one, im stuck here but i have

ln5 (3+x) = ln 20 (x-3)

3 ln5 + x ln5 = x ln20 - 3 ln20

3 ln5 + 3 ln20 = x(ln20 - ln5)