# Use the sleep dataset:
#
# https://stat.ethz.ch/R-manua1/R-deve1/library/datasets/htm1/sleep.html
#
par(mfrow=c(2,1))
plot( density( sleep$extra ), xlab='sleep', main='' )
plot( density( sleep$extra^2 ), xlab='sleep^2', main='' )
par(mfrow=c(1,1))