# t distribution
# =====================
# first plot standard normal in black
curve(dnorm(x), -4,4, main="red=2df,green=5df, blue=25df,black=z", ylab="density")

# now plot t curves with various degrees of freedom	
k <- 2 ; curve(dt(x, df=k), lty=k, add=TRUE, col=2)	#df = 2
k <- 5 ; curve(dt(x, df=k), lty=k, add=TRUE, col=3)	#df = 5
k <- 25 ; curve(dt(x, df=k), lty=k, add=TRUE, col=4)	#df = 25