install.packages("alr3")
library(alr3)
data(snake)
names(snake)
attach(snake)


fit2 = lm(Y ~ X-1)
fit2
summary(fit2)
sigma_sqhat = 1.7^2
sigma_sqhat


confint(fit2, level = 0.95)

#beta1hat = 0.520394
#sigma_sqhat = 2.89

fit1 = lm(Y ~ X)
fit1
summary(fit1)

par(mfrow=c(1,1))
plot(fit1$fitted,fit1$resid)
par(mfrow=c(2,2))
eda1(fit1$resid)
par(mfrow=c(1,1))
plot(fit2$fitted,fit2$resid)
par(mfrow=c(2,2))
eda1(fit2$resid)