# Precalc HELP, ASAP. No idea, Please explain

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#### danielh9103

Solve leaving answers in terms of e or ln.

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

b) 5^(3+x) = 20^x-3

#### 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.

superduper1

#### danielh9103

alright thank you!

is this correct:

5x - 3 = ln 10

5x = ln 10 + 3

x = [(ln 10) + 3] / 5

superduper1

Yep.

#### 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)

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