(adsbygoogle = window.adsbygoogle || []).push({}); 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.

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# Homework Help: Maxima and minima properties problem

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