2.19 ( ) Show that a real, symmetric matrix having the eigenvector equation (2.45) can be expressed as an expansion in the eigenvectors, with

2.19 ( ) Show that a real, symmetric matrix Σ having the eigenvector equation (2.45)

can be expressed as an expansion in the eigenvectors, with coefficients given by the eigenvalues, of the form (2.48). Similarly, show that the inverse matrix Σ−1 has a representation of the form (2.49).