[tex]\\~\qquad\quad S\ =\ 2PIR^2+2PIRH\\\underline{-2PIR^2\qquad-2PIR^2\qquad\quad\ }\\\\ S-2PIR^2=2PIRH\\\\ 2PIRH\ =\ S-2PIR^2\\\underline{ :(2PIR)\qquad :(2PIR)}\\\\\\ H=\dfrac{S-2PIR^2}{2PIR}\\\\\\ H=\dfrac{S}{2PIR}-\dfrac{2PIR^2}{2PIR}\\\\\\ H=\dfrac{S}{2PIR}-R[/tex]
or:
[tex]\\~\qquad\quad S\ =\ 2PIR^2+2PIRH\\\\~\qquad\quad S\ =\ 2PIR(R+H)\\\underline{:(2PIR)\qquad :(2PIR)}\\\\\\~\ \ \dfrac{S}{2PIR}\ =\ R+H\\\\\\ \dfrac{S}{2PIR}-R=H\\\\\\ H=\dfrac{S}{2PIR}-R[/tex]
