Re: Simple question: is it possible to take a derivative and solve for x ?
- To: mathgroup at smc.vnet.net
- Subject: [mg119310] Re: Simple question: is it possible to take a derivative and solve for x ?
- From: Robert Rosenbaum <robertr at math.uh.edu>
- Date: Mon, 30 May 2011 06:34:14 -0400 (EDT)
First, you seem to have used the reserved variable C as a parameter. You should rename it.
Second, it's highly unlikely that a closed form solution exists.
If you want to find the solutions, you'll have to instantiate the parameters and solve for each instantiation. For instance:
NSolve[(D[((x*l1 + (1 - x)*
l2)/((x^2*v1 + (1 - x)^2*v2 + 2*x*(1 - x)*c)^0.5)) + ((x*
L1 + (1 - x)*
L2)/((x^2*V1 + (1 - x)^2*V2 + 2*x*(1 - x)*cc)^0.5)), x] == 0)
/. {l1 -> 2, l2 -> 3, v1 -> 7, v2 -> 8, c -> 4, L1 -> 3, L2 -> 6, V1 -> 5, V2 -> 13, cc -> 3},
x]
gives three solutions, one of which is real. Note that I changed your variable C to cc.
Best,
Robert
On May 29, 2011, at 6:36 AM, Alonso wrote:
> I am a beginner, and would like to know if it is possible to solve for x the first derivative of a long equation in Mathematica. Bear with me, my background is in Biomedical Sciences.
>
> I am typing the following command:
>
> Solve[D[((x*l1 + (1 - x)*l2)/((x^2*v1 + (1 - x)^2*v2 + 2*x*(1 - x)*c)^0.5))+((x*L1 + (1 - x)*L2)/((x^2*V1 + (1 - x)^2*V2 + 2*x*(1 - x)*C)^0.5)), x]==0,x]
>
> But Mathematica 8 simply stops, and no output is given.
>
> Any tips?
>
> Cheers!
>
> Alonso
>