La-1l + LB + 3L = 0 for b-a-0.5

La-1l + LB + 3L = 0 for b-a-0.5

So A-1 = 0; B + 3 = 0; so a = 1, B = - 3, so b-a-0.5 = - 3-1-0.5 = - 4.5