If cos−1(1−x21+x2)+sin−1(2x1+x2)=K,∀xϵ[−1,0], then the value of K is
A
π2
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B
−π2
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C
0
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D
none of these
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Solution
The correct option is A0 Substituting x=tanA Hence cos−1(1−tan2A1+tan2A)+sin−1(2tanA1+tan2A) =cos−1(cos2A)+sin−1(sin2A) Now, xϵ[−1,0] Hence Aϵ[−π4,0] Therefore A lies in the fourth quadrant. Hence cos−1(cos2A) =2A And sin−1(sin2A) =−2A Therefore K=2A−2A =0