x=1:50
y=dnorm(x,20,5)
plot(x,y,type="l",col="red")
text(27,0.06,substitute(σ^2==5),col="red")
y1=dnorm(x,20,10)
lines(x,y1,type="l",col="blue")
text(37,0.017,substitute(σ^2==10))   #这里加上col="blue"为什么就不显示了呢？