Question

lnx=-2.046 help??

Answer 1

If you are trying to solve for x you need to isolate x. To do this here we need to get rid of the ln on the left side...how can we do this?

Answer 2

divide

Answer 3

Only problem with division here is that ln is a defined function itself, so dividing it does no good.

Answer 4

so instead you would do e^-2.046 right??

Answer 5

Yes :) You would take e to the power of both sides get what you said on the right, and since e is the inverse of ln, they cancel and form 1.

Answer 6

oh ok cool :) thanks! do you think you could help me with one more?

Answer 7

Sure.

Answer 8

The temp of an ingot upon being immersed in water kept at 20 degrees Celcius is 20+670e^-5t after t minutes. How long will it take for the temp to reach 25 degrees celcius?

Answer 9

for starters, do you know what formula i need to use?

Answer 10

The formula is given. 20+670e^(-5t)=desired temp.

Answer 11

20+670e^(-5t)=25

Answer 12

ohh ok

Answer 13

So you need to do the same thing. Isolate t since that is what it is asking for.

Answer 14

so first i subtract 20 right?

Answer 15

Yes :)

Answer 16

so the next steps would be:
ln670+lne^(-57)=ln5
and then would you move the -5t in front of the lne?

Answer 17

You want to take 5 and divide by 670. This will leave you with e^(-5t)=5/670 From here you can do the opposite of last time, which you got right, take the ln of both sides leaving -5t=ln(5/670)

Answer 18

oh ok! so i would get -0.992 as the final answer correct?

Answer 19

um i dont think i did the last step correctly?

Answer 20

I got about .980 seconds...remember time will never be negative and you can always plug your answer back in to see if it comes out right.

Answer 21

ok ok i see what i did wrong thanks! :)

Answer 22

No problem. :)