1. then: c,d ?1. If c,d = 1, then (a+b) = 3. By trying a = 1 or 2 and b = 1 or 2, and substituting in the equation (3 a ?1)(3 b ?1) = (5 c ?1;Since a,b,c and d are positive integers, in order for the inequalities b?a and c?d to be valid, then b?1 and d?1, a?1 and c?1 and since c=d
2. then (a+b) = 3. By trying a = 1 or 2 and b = 1 or 2, and substituting in the equation (3 a ?1)(3 b ?1) = (5 c ?1;Alternatively (and without proving that c=d), if d=1 and c=1, and since (a+b) = (1.5c+1.5d)