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Math Help - equation of semi circle

  1. #1
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    equation of semi circle

    what is the equation of a semi circle with:

    -diameter of 6
    -amplitude of 3
    -starting at the x-axis
    -the center is at (5,0)

    and what is the generic equation of a semi circle?
    thank you
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  2. #2
    Super Member 11rdc11's Avatar
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    Put your info into the standard equation of a circle


    \frac{(x-5)^2}{9} + \frac{y^2}{9} =1

    and then solve for y and that will give you the equation to a semi circle

    y = \pm \sqrt{9-(x-5)^2}
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  3. #3
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    what is the first formula that you showed? i'm not familiar with it
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  4. #4
    Super Member 11rdc11's Avatar
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    (x-a)^2 + (y-b)^2 = r^2

    a and being your center points respectively (5,0)
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  5. #5
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    oh ok i see it now. sorry, thank you very much though, that helped me out. do you by anychance know how to set restrictions on lines so that it only graphs a segment?
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  6. #6
    Super Member 11rdc11's Avatar
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    Nope but when you find out let me know to please. Still haven't figured out how to do it on my TI89
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  7. #7
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    that's exactly what i'm trying to figure out. i'm trying to find the way to set up a domain and range on it and i still can't lol. i'll make sure to tell you if i find something. this is for a project due thursday =p
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  8. #8
    Senior Member bkarpuz's Avatar
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    In parametric form, you may let \cos(t)=\frac{x-5}{3} and \sin(t)=\frac{y}{3} to get \alpha(t)=(x(t),y(t))=(3\cos(t)+5,\sin(t)) for t\in[0,\pi].
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