The matrix calculation is taking presently more and more a great place in teaching as well as in research. The matrix properties are treated basically, the statement leads the reading progressively, from definition to different matrix types as well as to linear equation systems, to proper value problems and to differential equation systems resolution. The matrix calculation interests many mathematicians, Physicists, economists and so on. This work is aiming at studying squared matrix proper values determination, its inverse with Leverrier’s algorithm, obliges determinant notions Knowledge beforehand.