A set of linear equations is given in the form Ax = b, where A is a 2 × 4 matrix with real number entries and b ≠ 0. Will it be possible to solve for x and obtain a unique solution by multiplying both left and right sides of the equation by AT (the super script T denotes the transpose) and inverting the matrix AT A? Answer is

• A. Yes, it is always possible to get a unique solution for any 2 × 4 matrix A.
• B. No, it is not possible to get a unique solution for any 2 × 4 matrix A.
• C. Yes, can obtain a unique solution provided the matrix AT A is well conditioned
• D. Yes, can obtain a unique solution provided the matrix A is well conditioned.