curve(dchisq(x, df = 2), from = 0, to = 40)
curve(dchisq(x, df = 5), from = 0, to = 40,col = "green", add = TRUE)
curve(dchisq(x, df = 10), from = 0, to = 40,col = "red", add = TRUE)
curve(dchisq(x, df = 30), from = 0, to = 40,col = "orange", add = TRUE)
legend("topleft", legend = paste0("DF = ", c(2, 5, 10, 30)),
       col = c("black", "green", "red", "orange"),
       lty = 1, lwd = 2)