9. In Problem 7(a}, let Yl and Y2 be the dual variables. Determine whether the following pairs of primal-dual solutions are optimal:

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(a) (Xl = 3,X2 = l;Yl = 4'Y2 = 1)

(b) (XI = 4, x2 = 1; YI = 1, Y2 = 0)

(c) (XI = 3, X2 = 0; YI = 5, Y:z = 0)