The radius of a sphere is 21 cm. Find the volume of a spherical wedge whose lune base angle is 90 degree.
-------------------------------------------------------------------------
A spherical wedge is a solid formed by revolving a semi-circle about its diameter by less than 360°.
Spherical Lune is the curve surface of the wedge, it is a surface formed by revolving a semi-circular arc
about its diameter by less than 360°.
See more at: http://www.mathalino.com/reviewer/solid-mensuration-solid-geometry/spherical-wedge-and-spherical-lune.
The volume of this "solid body" is one fourth of the volume of the sphere of the radius 21 cm:
V = . = ..