Consider the 3-by-2 matrix -21 0 -3 0 -2 A = 1 First compute the product AT A. Let X be an unknown variable and write down the 2-by-2 matrix AT A - XI. Compute the determinant det (ATA - XI) using the formula for 2-by-2 determinants (product of diagonal elements minus product of off-diagonal elements). You will get a quadratic polynomial in A. Solve for its two roots 0 < A