6. are shown in the following figure, please prove that(10%)

4. Let Mn is the nxn matrix with 3's on the main diagonal except the first entry which is 1, 1's directly above the main diagonal and (-1's directly below the main diagonal, and O's elsewhere. For example, We define Dn = det(Mn). Please (a) Find D1, and D2, (b) If n ≥ 3, find a formula for Dn in terms of, (c) Find a formula for Dn in terms of n. (15%)