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ta123

  • 4 years ago

need help on the attachment

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

  3. ta123
    • 4 years ago
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    no

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

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

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

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

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

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

  10. LagrangeSon678
    • 4 years ago
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    okay good

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

  12. ta123
    • 4 years ago
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    square root of 2

  13. ta123
    • 4 years ago
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    is it right?

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

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

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

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

  18. LagrangeSon678
    • 4 years ago
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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

  19. LagrangeSon678
    • 4 years ago
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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)

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

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

  22. ta123
    • 4 years ago
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    how come?

  23. LagrangeSon678
    • 4 years ago
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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

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

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

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

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

  28. ta123
    • 4 years ago
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    ok

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

  30. LagrangeSon678
    • 4 years ago
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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

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

  32. LagrangeSon678
    • 4 years ago
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    are we good?

  33. ta123
    • 4 years ago
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    36??

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

  35. LagrangeSon678
    • 4 years ago
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    yes?

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

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

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

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

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

  41. LagrangeSon678
    • 4 years ago
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    sure

  42. ta123
    • 4 years ago
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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

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

  44. ta123
    • 4 years ago
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    huh?

  45. ta123
    • 4 years ago
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    what negative sign?

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

  47. LagrangeSon678
    • 4 years ago
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    got it ?

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

  49. LagrangeSon678
    • 4 years ago
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    yes there was

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

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

  52. LagrangeSon678
    • 4 years ago
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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

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

  54. ta123
    • 4 years ago
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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

  55. LagrangeSon678
    • 4 years ago
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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

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

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

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

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

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

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

  62. LagrangeSon678
    • 4 years ago
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    anytime

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