Eigenvalues are useful in various areas of mathematics, such as in testing the critical values of a multi variable function to see if it is a local extrema. One of the more common ways to define eigenvalues is:
Definition (1): Given that A is an n by n matrix, λ is an eigenvalue of A if and only if det(A - λIn) = 0. Any nonzero vector in Null(A - λI) is called an eigenvector associated with λ
