Social Work homework help. Please help me with the following questions in linear algebra. Many thanks! 3. A matrix S is non-negativede?nite if CTSC Z O for any vector c. Prove that all covari-ance matrices are non-negativede?nite. If CTSC > 0 the matrix is positive de?nite.Show that a positive de?nite matrix is invertible. Also, give an example of a covariance matrix that is not positive de?nite. 4. Let 2 be a random vector of length n that has a M VN (0n,In) distribution. Let y : AZ + b. Derive ys moment generating function. What is ys distribution? 5. Let 2 be a random vector of length n that has a M VN (OMIR) distribution. LetU : ZTZ. Show that Us moment generating function is (1 273)_/2 (for 1 215 > 0).This is the MGF for a distribution that has two names. What are they, and what are their parameters?