Abstract Algebra 70: The orbit-stabilizer theorem 

Abstract Algebra 70: The orbit-stabilizer theorem
Abstract: We wrap up our sequence of videos on orbits and stabilizers by precisely stating the orbit-stabilizer theorem. We also give a partial outline of its proof, which relies on Lagrange's theorem (the size of a subgroup always divides evenly into the size of a finite group). The orbit-stabilizer theorem can be used, for example, to coun the number of rotational symmetries of a cube.
This video accompanies the class "Introduction to Abstract Algebra" at Colorado State University:
www.math.colostate.edu/~adams...