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Math Help - quadratic equations?

  1. #1
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    quadratic equations?

    AT is a tangent at T to a circle, centre O.
    OT = x cm AT = (x+5) cm OA = (x+8) cm
    a) Show that x^2-6x-39=0
    b) Solve the equation x^2-6x-39=0 to find the radius of the circle

    Give your answer correct to 3 significant figures.

    Someone please help.
    Last edited by alice; November 12th 2008 at 10:08 AM.
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  2. #2
    A riddle wrapped in an enigma
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    Quote Originally Posted by alice View Post
    AT is a tangent at T to a circle, centre O.
    OT = x cm AT = (x+5) cm OA = (x+8) cm
    a) Show that x^2-6x-39=0
    I think you probably meant to say: Show that (x+8)^2=x^2+(x+5)^2

    x^2+16x+64=x^2+x^2+10x-25

    x^2-6x-39=0
    Quote Originally Posted by alice View Post
    b) Solve the equation x^2-6x-39=0 to find the radius of the circle

    Give your answer correct to 3 significant figures.
    The quadratic will not factor, so use the quadratic formula to solve. Use only the positive root and round to 3 sig digits.

    I got x=\frac{6+\sqrt{192}}{2}\approx 9.93
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