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Quadratic formula question

  • #1

Homework Statement


.002x - .000001x^2 = .50



Homework Equations


-b+-sq.rt.((b^2)-(4ac))/2a



3. The Attempt at a Solution
Plugging a=-.000001, b=.002, and c=-.5 does not get the the correct answer. x is supposed to be 292.89. I can't remember any other way of going about trying to get this answer. Any suggestions?
 

Answers and Replies

  • #2
240
2
The formula is

( -b +- sqrt(b^2-4ac))/(2a)
 
  • #3
Mentallic
Homework Helper
3,798
94
As elibj123 said, the quadratic formula has a [itex]\pm[/itex] to consider. There are two solutions to any quadratic.

So you need to solve [tex]x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}[/tex]

You'll get your solution of 292.89 if you take [tex]x=\frac{-b-\sqrt{b^2-4ac}}{2a}[/tex]

but you'll also get a solution of approx 1700 if you solve [tex]x=\frac{-b+\sqrt{b^2-4ac}}{2a}[/tex]

Both solutions are correct, and you can check this by substituting your values of x back into the original equation .002x - .000001x^2 = .50
If your values of x are correct, the Left-hand side should approximately equal the right-hand side (depending on the approximation of your values of x).
 

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