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Question
cos1x=tan11x2x, then:
 
Options:
A .  X∈R
B .  −≤x≤1,x≠0
C .  0
D .  None of these
Answer: Option C
:
C
Putting θ=cos1x in R.H.S., we have
R.H.S =tan11x2x=tan11cos2θcosθ(0θπ)=tan1sinθcosθ=tan1tanθ=θ=cos1x when π2<θ<π2
i.e., when 0θ<π2
i.e., when 0<cosθ1 i.e., 0<x1.

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