\documentclass{article}
\begin{document}
Below are GET variables passed in the URL:
<<>>=
if(exists("GET"))
    print(GET)
@
\[ F(b) - F(a) = \int_a^b f(x)dx \]
<<fig=TRUE, keep.source=TRUE>>=
     # From ?persp
     y <- x <- seq(-10, 10, length= 30)
     f <- function(x,y) { r <- sqrt(x^2+y^2); 10 * sin(r)/r }
     z <- outer(x, y, f)
     z[is.na(z)] <- 1
     persp(x, y, z, theta = 30, phi = 30, expand = 0.5)
@
\end{document}