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Math Help - finding an angle in a circle given a point of (0.6, Y)

  1. #1
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    finding an angle in a circle given a point of (0.6, Y)

    Basic a unit circles is given
    ______
    | / (0.6,Y)
    | /
    | /
    |A)________

    Find angle A and Y, two decimal place

    So far I got this

    Since point is =(cosA,sinA), Y must equal to (Sin angle A)
    Then how would you find angle A. No radius or arc length is given! please help.
    Last edited by jepal; April 6th 2009 at 11:19 AM.
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  2. #2
    A riddle wrapped in an enigma
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    Quote Originally Posted by jepal View Post
    Basic a unit circles is given
    ______
    | / (0.6,Y)
    | /
    | /
    |A)________

    Find angle A and Y, two decimal place

    So far I got this

    Since point is =(cosA,sinA), Y must equal to (Sin angle A)
    Then how would you find angle A. No radius or arc length is given! please help.
    Hi jepal,

    \cos A =.6

    This means that \cos A=\frac{x}{r}=\frac{6}{10}=\frac{3}{5}

    x=3
    r=5

    Use the Pythagorean Theorem to find y.

    r^2=x^2+y^2

    5^2=3^2+y^2

    y=4

    So \sin A = \frac{y}{r}=\frac{4}{5}=.8

    Your point is (.6, .8)

    Your angle is \cos^{-1}\frac{3}{5} \ \ or \ \ \sin^{-1}\frac{4}{5} or approximately 53.1^{\circ}
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  3. #3
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    Quote Originally Posted by masters View Post
    Hi jepal,

    \cos A =.6

    This means that \cos A=\frac{x}{r}=\frac{6}{10}=\frac{3}{5}

    x=3
    r=5

    Use the Pythagorean Theorem to find y.

    r^2=x^2+y^2

    5^2=3^2+y^2

    y=4

    So \sin A = \frac{y}{r}=\frac{4}{5}=.8

    Your point is (.6, .8)

    Your angle is \cos^{-1}\frac{3}{5} \ \ or \ \ \sin^{-1}\frac{4}{5} or approximately 53.1^{\circ}
    Thank you, but how did u get 10, is it an assumption that radius is 10?
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  4. #4
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    Quote Originally Posted by jepal View Post
    Thank you, but did I just assume radius is 10, when no radius is given!
    What is the fractional form of the decimal number "0.6"?
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  5. #5
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    i figured that was the answer, but what is r then? im so confused! wouldnt it be

    cos A=x/r

    cos A=06./r? no? Please explain. Thanks
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