Dear all, 
I want to equalize a symbolic derivative (of a function with two
variables) with zero and convert it to a variable, e.g. x.
 
I'm computing the derivative by: (found it in the archive)
library(Ryacas)
f <- function(x,y) (100-x-y)*x-10*x
yacas(f) # register f with yacas
Df <- f
body(Df) <- yacas(expression(deriv(f(x,y),x)))[[1]]
Df
 
R-Output:
function (x, y) 
100 - x - y - x - 10
 
Questions : 
1.	How can I equalize the derivative(140-x-y-x-20) with zero?
2.	How can I convert it to x?
 
I want something like: 
45-0.5*y=x
 
With only one variable or two non-symbolic variables it's working with
uniroot(f, c(-10, 10))$root.
 
Thank you!
 
Immanuel Seeger
 
 
 
 

	[[alternative HTML version deleted]]

