Wednesday, April 8, 2009

Trigonometry Q

You are standing 15 m away from a post, and looking a bulb at the top of it, with an angle of 45 degrees. A friend is standing 60 degrees to your right, and looks at the same bulb at an angle of 65 degrees.

1. How high is the bulb?
2. What is the straight-line distance between your friend and the bulb at the top of the post?
3. How far (in meters) are the two of you standing from each other?


Cosine Rule:
a2 = b2 + c2 - 2 b c cos(A)
b2 = c2 + a2 - 2 c a cos(B)
c2 = a2 + b2 - 2 a b cos(C)
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8 comments:

  1. AnonymousApril 9, 2009 at 7:22 AM

    (1) using trigs
    tan 45 = height/15
    height = 15 tan 45
    height = 24.29m

    ReplyDelete
  2. AnonymousApril 9, 2009 at 7:27 AM

    (2) sin 65 = 24.29/distance
    distance= 24.29/sin 65
    distance= 29.37m

    ReplyDelete
  3. AnonymousApril 9, 2009 at 7:35 AM

    (3) using cosine rule
    a^2=b^2+c^2-2bc cosA
    a^2=15^2+15^2-2(15)(15) cos60
    a^2=450-450cos60
    a^2=450+482.58
    a^2=932.58
    a=30.5
    therefore distance = 30.5m

    ReplyDelete
  4. creApril 9, 2009 at 3:49 PM

    3.cosine rule
    a^2=b^2+c^2-2bc cosA
    a^2=15^2+15^2-2(15)(15) cos60
    a^2=450-450cos60
    a^2=450+482.58
    a^2=932.58
    a=30.5
    d=30.5m

    ReplyDelete
  5. WeezyApril 9, 2009 at 6:42 PM

    Diplomat`
    correct`set`but`Wrong`answers

    set`your`calculator`to`Degrees

    ReplyDelete
  6. starApril 21, 2009 at 5:42 PM

    1) tan45=height15
    height=15tan45
    =24.3meters

    ReplyDelete
  7. starApril 21, 2009 at 5:45 PM

    2)
    tan65=24.3m
    distance=24.3/sin65
    =29.4m

    ReplyDelete
  8. starApril 21, 2009 at 5:50 PM

    3)
    Cosine rule
    a^2=b^2+c^2-2bc cosA
    a^2=15^2+15^2-2(15)(15)cos60
    a^2=450-450cos60
    a^2=450+482.58
    a^2=932.58
    a=30.5

    distance=30.5

    ReplyDelete

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