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onegirl

  • one year ago

A person scores f(x) = 90/1 + 4e^-0.4t points on a test after t hours of studying. What does the person score without studying at all? Compute f’(0) and estimate how many points 1 hours of studying will add to the score.

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  1. onegirl
    • one year ago
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    This is what I did but my teacher said it was wrong she said ( Find f' and f'(0).) F(x) = 90/ 1 + 4e^-0.4t F(0) = 90/ 1 + 4e^-0.4(0) = 18 F(1) = 90/1 + 4e^-0.4(1) = 24.45 So comparing the scote at f(1) and f(0) where at f(1) studying for 1 hour and f(0) studying none. F(1) - f(0)/24.45 – 18 = 6.45 points

  2. EulersEquation
    • one year ago
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    Should this have parenteses or not? Is this F(x) = 90/ (1 + 4e^-0.4t )?

  3. onegirl
    • one year ago
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    yes prenthesis

  4. onegirl
    • one year ago
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    like this \[\frac{ 9 }{ 1 + 4e ^{-0.4t}}\]

  5. EulersEquation
    • one year ago
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    Your teacher specifically said to differentiate?

  6. onegirl
    • one year ago
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    yes

  7. onegirl
    • one year ago
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    she said to Find f' and f'(0)

  8. onegirl
    • one year ago
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    @EulersEquation so do you know how?

  9. onegirl
    • one year ago
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    @Numb3r1 can u help?

  10. EulersEquation
    • one year ago
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    Yes. I need to review this. First glance is to use the quotient rule. Do you know how to use the quotient rule? Someone else may want to take a look. I am in the middle of helping someone else. When I finish I'll get on it.

  11. onegirl
    • one year ago
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    ok

  12. EulersEquation
    • one year ago
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    Ha! I am terrible at arithmetic. On first run I get a negative number for f'(0). You cannot make a negative score on a test! Unless the teacher doesn't like you. I am rusty on this. I'll work on it some more. In the meantime, bump the problem and hopefully someone else will tackle this.

  13. onegirl
    • one year ago
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    okay

  14. onegirl
    • one year ago
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    @waterineyes

  15. waterineyes
    • one year ago
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    Just want to take derivative of that??

  16. onegirl
    • one year ago
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    yes Find f' and f'(0)

  17. waterineyes
    • one year ago
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    It will come out to be negative..

  18. onegirl
    • one year ago
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    what will come out? so what i did above is wrong or?

  19. waterineyes
    • one year ago
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    Wait, let we do it first..

  20. waterineyes
    • one year ago
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    \[\frac{ 90 }{ 1 + 4e ^{-0.4t}} = \frac{ -(90)(-1.6 \cdot e^{-0.4t}) }{ (1 + 4e ^{-0.4t})^2}\]

  21. waterineyes
    • one year ago
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    It will become positive now.. :)

  22. onegirl
    • one year ago
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    okay

  23. EulersEquation
    • one year ago
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    Yeah. I don't see why it has to be differentiated -- not according to the question.

  24. waterineyes
    • one year ago
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    Am I right in this?

  25. EulersEquation
    • one year ago
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    Ah! I forgot to square the denominator!

  26. EulersEquation
    • one year ago
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    That looks good.

  27. onegirl
    • one year ago
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    okay thanks!

  28. waterineyes
    • one year ago
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    So you can now find f'(0) by putting 0 as value of t..

  29. onegirl
    • one year ago
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    okay

  30. waterineyes
    • one year ago
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    @onegirl can you go for that?

  31. onegirl
    • one year ago
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    just plug in 0 and solve right?

  32. waterineyes
    • one year ago
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    Yep, just simple calculations with calculator..

  33. onegirl
    • one year ago
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    okay yes i can

  34. waterineyes
    • one year ago
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    Good.. Keep it up..

  35. onegirl
    • one year ago
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    i got 0 after i solved

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