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Re: Derivatives

• To: mathgroup at smc.vnet.net
• Subject: [mg113742] Re: Derivatives
• From: Walking Randomly <michael.p.croucher at googlemail.com>
• Date: Wed, 10 Nov 2010 06:28:02 -0500 (EST)
• References: <ib8csf$2fb$1@smc.vnet.net>

On Nov 8, 8:37 am, will <will.yeu... at gmail.com> wrote:
> Hello,
>
> I am trying to take the derivative (d/dx) of a very messy equation
> that is more easily expressed initially as a function of y, then y and
> a function of x. Rather than have to substitute and expand, can a set
> of equations be input  and instructed to find a derivative wrt x?
>
> (A little bit new to Mathematica)
>
> Thanks.
> Will

Hi

You can tell Mathematica that y is a function of x by doing y[x].  For
example, say we wanted to differentiate x=Sqrt[y] where y is a
function of x.  You can do this has follows

D[x == Sqrt[y[x]], x]

Stare at the answer for a bit and you'll see that it gives a result
consistent with what we'd get if we took y=x^2 and differentiated.

Cheers,
Mike
www.walkingrandomly.com