R: plotting multiple functions

Hi all

Another simple question.

I would like to plot three graphs one the same plot with different
colours. Say red, blue and black. Here are the functions.

r1<-1+5*cos(2*pi*seq(1:100)/20)+rnorm(100)
r2<-1+7*sin(2*pi*seq(1:100)/20)+rnorm(100)
r3<-1+7*sin(2*pi*seq(1:100)/20)+5*cos(2*pi*seq(1:100)/20)+rnorm(100)

Regards
Allan