三个图，legend（）和text（）的部分是出了什么问题，怎么运行不出来？请牛人赐教！急!
x=c(seq(0,10,length=1000));
y2=dchisq(x,2);
y3=dchisq(x,3);
y5=dchisq(x,5);
plot(x,y2,type="l",xlab="",ylab="",lty=1,main=expression(paste(chi^2,"Distribution")));
lines(x,y3,type="l",xlab="",ylab="",lty=2);
lines(x,y5,type="l",xlab="",ylab="",lty=3);
text(locator(3),c(expression(chi^2*(2)),expression(chi^2*(3)),expression(chi^2*(5))));




x=c(seq(-4,4,length=1000));
y2=dnorm(x);
y3=dt(x,2);
y5=dt(x,1);
plot(x,y2,type="l",xlab="",ylab="",lty=1,main="");
lines(x,y3,type="l",xlab="",ylab="",lty=2);
lines(x,y5,type="l",xlab="",ylab="",lty=3);
legend(-4,.4,c("N(0,1)","t(2)","t(1)",lty=1:3);
text(locator(3),c("N(0,1)","t(2)","t(1)"))



x=c(seq(0,4.5,length=1000));
y2=df(x,50,20);
y3=df(x,10,20);
y5=df(x,3,20);
plot(x,y2,type="l",xlab="",ylab="",lty=1,main="");
lines(x,y3,type="l",xlab="",ylab="",lty=2);
lines(x,y5,type="l",xlab="",ylab="",lty=3);
legend(3,1.1,c("F(50,20)","F(10,20)","F(3,20)",lty=1:3);
text(locator(3),c("F(50,20)","F(10,20)","F(3,20)"))