curve(df(x, 3, 15, ncp=0), col="blue", xlim=c(0,5), ylim=c(0,1), xlab="f", ylab="f(f)")
curve(df(x, 5, 15, ncp=0), add=T, col="red", xlim=c(0,5), ylim=c(0,1), xlab="f", ylab="f(f)")
curve(df(x, 10, 15, ncp=0), add=T, col="green", xlim=c(0,5), ylim=c(0,1), xlab="f", ylab="f(f)")
curve(df(x, 15, 15, ncp=0), add=T, col="black", xlim=c(0,5), ylim=c(0,1), xlab="f", ylab="f(f)")

df1_list<-c(3,5,10,15)
df2_list<-c(15,15,15,15)
par(mfrow=c(2,2))


for (i in 1:length(df1_list)) {
  curve(df(x, df1=df1_list[i], df2=df2_list[i], ncp=0), xlim=c(0,5), ylim=c(0,1), xlab="f", ylab="f(f)", main=paste("df1=", df1_list[i], "df2=", df2_list[i]))
}