2.5 Let X1, X2, X3 denote changes in the incidence of crime from 1967 to 1968, for three types of crime. Suppose there is so much data available that the matrix of variances and covariances of (X1,X2,X3) is known to be given approximately by Find –1. Show by numerical computation that –1 is positive definite. Interpret the negative signs in .