omega = 1 # s^-1
X     = 1 # cm
phi   = 0

T = 2*pi/omega

t <- seq(0, 2*T, len=201)

old.mar = par("mar")
par(mar=c(4.2,4,2.6, 0.3))
plot(t, X*cos(omega*t+phi), ty='l', col='blue', lwd=2,  
     ylim=c(-1,1.2), xlab='t  (s)', ylab='x  (cm)',
main = "x(t) = X*cos(omega*t+phi);  X=1cm, omega=1s^-1")
points(t, omega*X*cos(omega*t+phi+pi/2), ty='l', col='cyan', lwd=2)
points(t, omega^2*X*cos(omega*t+phi+pi), ty='l', col='red', lwd=2)
text(1.,1.12, "phi=0", col='blue', cex=2)
text(4.7,1.12, "phi=pi/2", col='cyan', cex=2)
text(9.5,1.12, "phi=pi", col='red', cex=2)
par(mar=old.mar)