Question

If a1, a2, a3……..  are in AP then if a7 = 15, then the value of common difference that would make a2 a7 a12 greatest is?

(a) 2

(b) 0

(c) 4

(d) 9

I got this question by my school teacher while I was bunking the class.

Asked question is from Arithmetic and Geometric Mean topic in division Basic Structures: Sets, Functions, Sequences, Sums and Matrices of Discrete Mathematics

Answer 1

Right option is (b) 0

To explain: Let d be common difference of the AP. Then,

a2 a7 a12 = (15 – 5d)(15)(15 + 5d) = 375(9 – d^2)

For maximum value d=0.