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March 25, 2017

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Hi this is a dimensional analysis problem,I want to solve for x.

300x^2 -16.667x^3+(-7200)=0

after getting
300x^2 -16.667x^3=7200
I really don't know what to do.

Plz help.

  • Math (Dimensional Analysis) - ,

    This is very effective online webpage.
    I simply entered the equation in the form

    300x^2 -16.667x^3-7200 = 0

    http://www.wolframalpha.com/input/?i=300x%5E2+-16.667x%5E3-7200+%3D0

    It gave my 3 real answers and the corresponding gram of
    f(x) = 300x^2 -16.667x^3-7200

  • Math (Dimensional Analysis) - ,

    Let the 16.667 be treated at 16 2/3. Then

    900 x^2 -50 x^3 -21600 = 0

    One root of that equation is exactly x = 6. Call it a lucky guess.

    Divide the cubic by (x-6) to get an easily solved quadratic, for the other two roots. It can be reduced to

    x^2 -120 x -72 = 0

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