$h_{ii} = \frac{1}{n} + \frac{(x_i - \bar{x})^2}{\sum (x_j - \bar{x})^2}$

$h_{ii} = \frac{1}{n} - \frac{(x_i - \bar{x})^2}{\sum (x_j - \bar{x})^2}$

$h_{ii} = \frac{\sum (x_j - \bar{x})^2}{(x_i - \bar{x})^2}$

$h_{ii} = \frac{x_i^2}{\sum x_j^2}$