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Math Help - Finding roots

  1. #1
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    Finding roots

    I'm not sure if this is the right forum, but this was in my calculus class.

    f(x) = (16x+50x^3) - 40^3

    I need to find the roots. And I want to find the precise roots, without a decimal.

    Guess and check, and graphing result in a root of ~10.845
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  2. #2
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    make f(x)=0, so 0= (16+50x^3)-40^3

    0= (16+50x^3)-64000

    0= 50x^3-63984

    Now solve for x.
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  3. #3
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    Quote Originally Posted by ankhmor View Post
    I'm not sure if this is the right forum, but this was in my calculus class.

    f(x) = (16x+50x^3) - 40^3

    I need to find the roots. And I want to find the precise roots, without a decimal.

    Guess and check, and graphing result in a root of ~10.845
    Why, where has this come from and are you sure that you have posted it correctly?

    If you want the closed form roots of what you have posted you will need to use Cardarno's method for the roots of the depressed cubic, which is about halfway down >>this<< page

    CB
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  4. #4
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    Quote Originally Posted by pickslides View Post
    make f(x)=0, so 0= (16+50x^3)-40^3
    pickslides, the equation was (16x+ 50X^3)- 40^3= 0 which becomes
    50x^3+ 16x- 64000= 0, rather more difficult to solve.

    0= (16+50x^3)-64000

    0= 50x^3-63984

    Now solve for x.
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