Help on calculating mean for variance()

[bobhancock]

Assuming R^2 for the example coordinates (x, y).

Points [ 3, 4
5, 6]

Centroid [ 4, 5]

is the mean of x = [(4 - 3) + (4 - 5)] / 2 ?

Or do we need to square it as in [ (4 - 3) ^2 + (4 - 4)^2 ] / 2 and then take the square root?