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smurfy14

  • 5 years ago

lnx=-2.046 help??

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  1. anonymous
    • 5 years ago
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    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?

  2. smurfy14
    • 5 years ago
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    divide

  3. anonymous
    • 5 years ago
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    Only problem with division here is that ln is a defined function itself, so dividing it does no good.

  4. smurfy14
    • 5 years ago
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    so instead you would do e^-2.046 right??

  5. anonymous
    • 5 years ago
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    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.

  6. smurfy14
    • 5 years ago
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    oh ok cool :) thanks! do you think you could help me with one more?

  7. anonymous
    • 5 years ago
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    Sure.

  8. smurfy14
    • 5 years ago
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    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?

  9. smurfy14
    • 5 years ago
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    for starters, do you know what formula i need to use?

  10. anonymous
    • 5 years ago
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    The formula is given. 20+670e^(-5t)=desired temp.

  11. anonymous
    • 5 years ago
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    20+670e^(-5t)=25

  12. smurfy14
    • 5 years ago
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    ohh ok

  13. anonymous
    • 5 years ago
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    So you need to do the same thing. Isolate t since that is what it is asking for.

  14. smurfy14
    • 5 years ago
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    so first i subtract 20 right?

  15. anonymous
    • 5 years ago
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    Yes :)

  16. smurfy14
    • 5 years ago
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    so the next steps would be: ln670+lne^(-57)=ln5 and then would you move the -5t in front of the lne?

  17. anonymous
    • 5 years ago
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    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)

  18. smurfy14
    • 5 years ago
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    oh ok! so i would get -0.992 as the final answer correct?

  19. smurfy14
    • 5 years ago
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    um i dont think i did the last step correctly?

  20. anonymous
    • 5 years ago
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    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.

  21. smurfy14
    • 5 years ago
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    ok ok i see what i did wrong thanks! :)

  22. anonymous
    • 5 years ago
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    No problem. :)

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