0.8 0.1 0.1 4. Consider the matrix A = 0.1 0.6 0.3 . 0.1 0.3 0.6 12) Compute IAI, 12Al, and 21Al. Note that, for example, IAI denotes the determinant of A. 13) Determine if A is singular. If no, find its inverse. (Keep two decimal places if necessary). 14) Find the corresponding diagonal matrix D. 15) Suppose A represents the variance-covariance matrix of three random variables X, Y, and Z. Form three new variables which are uncorrelated with each other. (Keep two decimal places if necessary). 16) Compute the variances of the three new variables. 17) Find the corresponding quadratic function and determine its definiteness.