1. The problem statement, all variables and given/known data Let An be the nth term of an A.P. and if A7 = 15, then the value of the c.d. that would make A3 x A7 x A12 greatest is : 1)9 2)9/4 3)3/8 4)18 2. Relevant equations 3. The attempt at a solution Applying AM>=GM A3+A7+A12/3 >= (A3 x A7 x A12)^1/3 given that A+6d=15 therefore 3A+19d=45 The previous expression reduces to 45+d/3 >= (A3 x A7 x A12)^1/3 cubing the inequality. (45+d/3)^3 >= (A3 x A7 x A12) From the choices, 18 will make RHS greatest. But that is not correct! Any help appreciated.