how do I use the solver to solve polynomial equations?

I am using Excel 2000

It is possible to use the quadratic formula for quadratic equations of the
form ax^2+bx+c. Solving for values of x use: (-b +or -(sqroot(b^2-4ac))/2a

"Cameron PE" wrote:

> I am using Excel 2000

Nice in theory, bad idea in practice. Quoting (with slight editing for
this context) from Press, et al, /Numerical Recipes in C/:
<quote> If either a or c (or both) are small, then one of the roots will
involve the subtraction of b from a very nearly equal quantity (the
discriminant); you will get that root very inaccurately. The correct way
to compute the roots is
q = -(b + sgn(b)*sqrt(b^2-4a*c))*0.5

Then the two roots are
x1 = q/a and x2 = c/q
<end quote>

You can get this straight off of the web by searching for "Numerical
Recipes in C", then look for Chapter 5. section 6 (Quadratic and Cubic
Equations), pp 183 ff.

Harlan Grove and I (and perhaps Jerry Lewis) had a thread on this some
time back. I wrote the equations above to accommodate VBA to an extent.
You may be able to rearrange things to make for a snappier function
call, but you get the idea (I hope).

Regards,
Dave Braden

CJ wrote:
> It is possible to use the quadratic formula for quadratic equations of the
> form ax^2+bx+c. Solving for values of x use: (-b +or -(sqroot(b^2-4ac))/2a
>
> "Cameron PE" wrote:
>
>> I am using Excel 2000

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