JEE Main 2019 — Sequences And Series Question with Solution
From: JEE Main 2019 (Online) 12th January Evening Slot
Question
If sin4 + 4 cos4 + 2 = 4 sin cos ; , [0, ],
then cos( + ) cos( ) is equal to :
then cos( + ) cos( ) is equal to :
Choose an option
Show full solutionCorrect option: A
Correct answer
A
Step-by-step explanation
A.M. G.M.
sin4 + 4 cos2 + 2 4 sin cos
Given that sin4 + 4cos4 + 2 = 4 sin cos
A.M.=G.M. sin4 = 1 = 4 cos4
sin = 1, cos =
sin = as [0, ]
cos( + ) cos ( ) = 2 sin
=
sin4 + 4 cos2 + 2 4 sin cos
Given that sin4 + 4cos4 + 2 = 4 sin cos
A.M.=G.M. sin4 = 1 = 4 cos4
sin = 1, cos =
sin = as [0, ]
cos( + ) cos ( ) = 2 sin
=
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This is a previous-year question from JEE Main 2019, 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.