Exponential Functions:
Can someone show me how to solve this, with or without a calculator: 100 (1-e^(-0.08 t))-70

Question

anonymous · Answer

$$0=100(1-e ^{-0.08t})-70$$   a little cleaner

rob1525 · Answer

$$70=100 - 100e^-0.08t$$

rob1525 · Answer

subtract 100 and divide by -100

anonymous · Answer

the question is asking to solve for zero to get a decimal

rob1525 · Answer

you can find it with a graph or algebraicly

anonymous · Answer

i have the answer but i dont understand how they go it 15.04966

anonymous · Answer

graph it by pluggin in numbers for T?

rob1525 · Answer

Graph it with the t and then find when it crosses the x axis

anonymous · Answer

oh yes i see what you mea, that point will give me the answer

rob1525 · Answer

It sure will, would you like me to solve algebraicly?

anonymous · Answer

yes please, i wont have time to graph if I take a test

rob1525 · Answer

$$70-100=-100*e^-0.08t$$

rob1525 · Answer

$$-30/-100=e^-0.08t$$

anonymous · Answer

there is more?

rob1525 · Answer

sorry got disconnected. Yes.

rob1525 · Answer

Now use the natural log to bring down the exponent. the natural log undoes e.$$\ln(3/10)=\ln(e^-0.08t)$$

rob1525 · Answer

t= ln(3/10)/-0.08 = 15.049

anonymous · Answer

ok go it, I'm gonna right this down just to make sure i got it
thank you!

rob1525 · Answer

no prob ;)