(a) Find the determinant of the matrix A = 1 2 1 1 2210 3 6 1 21 00 u V Sketch in a uv-plane the set of points for which A has no inverse. Hence, or otherwise, show that when v> A has an inverse for all values of u. (b) Consider the two quadratic forms 9(xxx) = x + x + x XX3 (xxx)x+x+x-2xx Determine directly from the definitions whether each quadratic form is (1) positive definite, (11) positive semidefinite but not positive definite, (iii) neither of these.