Deduction of the area of a spherical skull-cap

It is very easy!! We apply the process by which there is calculated the value of a directly proportional magnitude to other one, ie, we use a rule of three direct.

We know area of a sphere is: {4.Pi.R^2}.So, we have to half a sphere the following:

{2.Pi.R^2} rightR
                                         ⇒    {x={2.Pi.R^2.h}/R}= tabular{11}{11}{{2.Pi.R.h}};-)
x          righth



being h the height of skull-cap and x the area that we want to calculate, ie, the mystery.