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ta123

need help on the attachment

  • 2 years ago
  • 2 years ago

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  1. ta123
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    • 2 years ago
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  2. LagrangeSon678
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    come on no has helped you with this yet?

    • 2 years ago
  3. ta123
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    no

    • 2 years ago
  4. LagrangeSon678
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    should i solve this or go to sleep.....

    • 2 years ago
  5. ta123
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    solve before going, please

    • 2 years ago
  6. ta123
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    Oops! forgot to sleep after going

    • 2 years ago
  7. LagrangeSon678
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    okay, first things first, lets find the first derivaitve of the function your where given

    • 2 years ago
  8. LagrangeSon678
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    can you find it?

    • 2 years ago
  9. ta123
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    9sec^(2)x

    • 2 years ago
  10. LagrangeSon678
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    okay good

    • 2 years ago
  11. LagrangeSon678
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    now can you please evaluate: f(pi/4)=9sec^2(pi/4)

    • 2 years ago
  12. ta123
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    square root of 2

    • 2 years ago
  13. ta123
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    is it right?

    • 2 years ago
  14. LagrangeSon678
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    basically to make it more accesible we can write this as: f(pi/4)=9[sec(pi/4)]^2

    • 2 years ago
  15. LagrangeSon678
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    further more we can write it as: f(pi/4)=9[1/cos(pi/4)]^2

    • 2 years ago
  16. LagrangeSon678
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    then evalutaing we get: f(pi/4)=9[1/sqrt(2)/(2)]^2

    • 2 years ago
  17. ta123
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    what square root 2/2???

    • 2 years ago
  18. LagrangeSon678
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    further: f(pi/4)=9[sqrt(2)]^2 which the gives us: f(pi/4)=9(2), which is 18 Thus f(pi/4)=18

    • 2 years ago
  19. LagrangeSon678
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    yes, look at the unit circle, at pi/4 or 45 degrees, cos is sqr(2)/2, now if we rationalize the numerator we get just sqrt(2)

    • 2 years ago
  20. ta123
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    oh, thought your doing sec

    • 2 years ago
  21. LagrangeSon678
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    i rewrote secx as 1/cosx

    • 2 years ago
  22. ta123
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    how come?

    • 2 years ago
  23. LagrangeSon678
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    just to make is easier for me, but if realise that sec(pi/4) is sqrt(2) then more power to you

    • 2 years ago
  24. LagrangeSon678
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    Now we have found the slope (m) of our line, it is 18

    • 2 years ago
  25. ta123
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    y-y=m(x-x)

    • 2 years ago
  26. LagrangeSon678
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    yes, but we will use this form, y=mx+b

    • 2 years ago
  27. LagrangeSon678
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    i am getting sleepy lets finish this problem

    • 2 years ago
  28. ta123
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    ok

    • 2 years ago
  29. ta123
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    what would be the b in the slope formula

    • 2 years ago
  30. LagrangeSon678
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    Now remeber we said, that we have the x coordinate in the beining of pi/4, lets evaluate the orginal function at this point, this will give us the y in our line. f(pi/4)=9tan(pi/4) =9(1) =9 now we have our x which is pi/4, we have our slope which is 18, lets plug this info into our line: 9=18(pi/4)+b this means that b is = to 9-18pi/4

    • 2 years ago
  31. LagrangeSon678
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    now lets substitute everyting in: y=18x-(36-18pi)/(4)

    • 2 years ago
  32. LagrangeSon678
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    are we good?

    • 2 years ago
  33. ta123
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    36??

    • 2 years ago
  34. LagrangeSon678
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    i combined 9 and 18pi/4

    • 2 years ago
  35. LagrangeSon678
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    yes?

    • 2 years ago
  36. ta123
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    still don't see how you can 36??

    • 2 years ago
  37. LagrangeSon678
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    |dw:1316152625201:dw|

    • 2 years ago
  38. ta123
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    you could've just simplify it to 9pi/2

    • 2 years ago
  39. LagrangeSon678
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    okay, then smarty pants do it your way, regardless we came to a correct answer

    • 2 years ago
  40. ta123
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    sorry, so the finally would look like this 18x+9(1-pi/2)

    • 2 years ago
  41. LagrangeSon678
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    sure

    • 2 years ago
  42. ta123
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    I just look the answer choices and so which one was the closest, but how come they have it 18x+9(1-pi/2) instead of just 18x+9pi/2

    • 2 years ago
  43. LagrangeSon678
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    distribute the negative sign, first

    • 2 years ago
  44. ta123
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    huh?

    • 2 years ago
  45. ta123
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    what negative sign?

    • 2 years ago
  46. LagrangeSon678
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    |dw:1316153351852:dw|

    • 2 years ago
  47. LagrangeSon678
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    got it ?

    • 2 years ago
  48. ta123
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    but was there a 9-18pi/4 at the beginning

    • 2 years ago
  49. LagrangeSon678
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    yes there was

    • 2 years ago
  50. LagrangeSon678
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    can you not see it: |dw:1316153548845:dw|

    • 2 years ago
  51. ta123
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    I meant why was 9-18pi/4 at the begginig

    • 2 years ago
  52. LagrangeSon678
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    above i accidentally wrote:y=18x-(36-18pi)/(4), but is was really suppose to be : y=18x+(36-18pi)/(4), sorry about the typo

    • 2 years ago
  53. LagrangeSon678
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    okay, so can we lay this problem to rest?

    • 2 years ago
  54. ta123
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    I guess, but still don't get why they have 9-18pi/4 plug into b instead of just 18pi/4 by itself

    • 2 years ago
  55. LagrangeSon678
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    Now remeber we said, that we have the x coordinate in the beining of pi/4, lets evaluate the orginal function at this point, this will give us the y in our line. f(pi/4)=9tan(pi/4) =9(1) =9 now we have our x which is pi/4, we have our slope which is 18, lets plug this info into our line: 9=18(pi/4)+b this means that b is = to 9-18pi/4

    • 2 years ago
  56. LagrangeSon678
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    |dw:1316153804630:dw|

    • 2 years ago
  57. ta123
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    oh, ok now we can lay this problem to rest, thanks so much for being patience

    • 2 years ago
  58. LagrangeSon678
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    its good you ask questions, i know i can confusing sometimes :)

    • 2 years ago
  59. ta123
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    Thanks for giving me a metal

    • 2 years ago
  60. ta123
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    yeah I just want to understand the problem instead of just getting the answer

    • 2 years ago
  61. ta123
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    because I might see it on the test, but thanks again

    • 2 years ago
  62. LagrangeSon678
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    anytime

    • 2 years ago
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