How to plot square inside sphere?

With reference to figure shown, ; instead of circle, I want to plot * *square on sphere* * . X,Y,Z values of 1 point in sphere coordinate I know. Keeping that point as center I want to plot square. Square size may be anything. But is it possible to plot square on sphere?

Please let me get the solution.. Thank you, in advaance..

[Roger Stafford]

Only the square's four vertices can lie on the sphere's surface. The four edges are necessarily inside.

[Andrew Newell]

There are two parts to this problem - the mathematical one of identifying four vertices on the sphere and the graphical one of plotting it. Since this forum is for help in MATLAB, you should solve the first part and then we can show you how to plot it.