JEE Main 2021 — Sequences And Series Question with Solution
From: JEE Main 2021 (Online) 1st September Evening Shift
Question
Let a1, a2, ..........., a21 be an AP such that . If the sum of this AP is 189, then a6a16 is equal to :
Choose an option
Show full solutionCorrect option: B
Correct answer
B72
Step-by-step explanation
(Given)
.... (1)
Now sum of first 21 terms =
a1 + 10d = 9 ..... (2)
For equation (1) & (2) we get
a1 = 3 & d =
or a1 = 15 & d =
So, a6 . a16 = (a1 + 5d) (a1 + 15d)
a6a16 = 72
Option (b)
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This is a previous-year question from JEE Main 2021, covering the Sequences And Series chapter of Mathematics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.