curve(df(x, df1=2, df2=2), from=0, to=5)
curve(df(x, df1=5, df2=5), from=0, to=5,col = "green", add = TRUE)
curve(df(x, df1=10, df2=10), from=0, to=5,col = "red", add = TRUE)
curve(df(x, df1=30, df2=15), from=0, to=5,col = "orange", add = TRUE)
legend("topright", legend = paste0("DF = ", c(2, 5, 10, 30)),
       col = c("black", "green", "red", "orange"),
       lty = 1, lwd = 2)