curve(dnorm(x,-2,1),xlim=c(-6,6),from=-6,to=2,col=1,lwd=1.5)
curve(dnorm(x,2,1),from=-2,to=6,add=T,col=2,lwd=1.5,lty=2)
abline(h=0,lwd=1.5)
abline(v=c(-2,2),col=1:2,lwd=1.5)
curve(dnorm(x,0,1),from=-6,to=6,xlim=c(-6,6),ylim=c(0,0.8),col=1,lwd=1.5)
curve(dnorm(x,0,2),from=-6,to=6,add=T,col=2,lty=2,lwd=1.5)
curve(dnorm(x,0,0.5),from=-6,to=6,add=T,col=11,lty=2,lwd=1.5)
abline(h=0,lwd=1.5)
abline(v=0,lwd=1.5)