From: Gabor Grothendieck <ggrothendieck_at_gmail.com>

Date: Mon, 28 Feb 2011 09:47:22 -0500

Date: Mon, 28 Feb 2011 09:47:22 -0500

On Mon, Feb 28, 2011 at 5:03 AM, zbynek.janoska_at_gmail.com
<zbynek.janoska_at_centrum.cz> wrote:

> Thanks,

*> Your advice solved the problem for one substitution, but I needed to
**> substitute twice: first s = (a+b+c)/2
**> and than c = sqrt(a^2 + b^2 -2*a*b*cos(gamma)) and I hoped I can do it
**> simultaneously
*

There is no limitation to the number of substitutions using Ryacas:

*> library(Ryacas)
*

> a <- Sym("a"); b <- Sym("b"); gamma <- Sym("gamma")

*> c <- sqrt(a^2 + b^2 -2*a*b*cos(gamma))
**> s <- (a+b+c)/2
**> deriv(s, a)
*

[1] "Starting Yacas!"

expression(2 * ((2 * a - 2 * b * cos(gamma))/(2 * root(a^2 +

b^2 - 2 * a * b * cos(gamma), 2)) + 1)/4)

-- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Mon 28 Feb 2011 - 15:08:59 GMT

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