Consider the simple linear regression model \(Y_i=\beta _0+\beta _1x_i+\epsilon _i\) (\(i=1,2,\ldots ,n\)). Assume independent \(N(0,\sigma ^2)\) errors.
(a) Find the least squares estimators \(\hat \beta _0\) of \(\hat \beta _1\) of \(\beta _0\) and \(\beta _1\).
(b) Calculate the covariance matrix of \((\hat \beta _0,\hat \beta _1)\).