If 0≤A≤π4, then tan−1(12tan2A)+tan−1(cotA)+tan−1(cot3A) is equal to
A
π4
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B
π
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C
0
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D
π2
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Solution
The correct option is Bπ tan−1(12tan2A)+tan−1(cotA)+tan−1(cot3A)=tan−1(12tan2A)+tan−1(cotA+cot3A1−cot4A)=tan−1(12⋅2tanA1−tan2A)+tan−1(cotA(1+cot2A)(1−cot2A)(1+cot2A))=tan−1(tanA1−tan2A)+tan−1(tanAtan2A−1)=tan−1(tanA1−tan2A)+tan−1(−tanA1−tan2A)=tan−1(tanA1−tan2A)+π−tan−1(tanA1−tan2A)=π+0=π