Posted by **Kari** on Thursday, November 24, 2011 at 1:55am.

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) -
**Reiny**, Thursday, November 24, 2011 at 11:27am
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) -
**drwls**, Thursday, November 24, 2011 at 4:22pm
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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