\cot 2 A=\frac{\cot ^{-} A-1}{2 \cot A} – InterviewSolution

1.	\cot 2 A=\frac{\cot ^{-} A-1}{2 \cot A}
Answer» tan2A=tan(A+A)=(tanA+tanA)/(1-tan^2A)tan2A=1/cot2AtanA=1/cotAso 1/cot2A=(1/cotA+1/cotA)/(1-1/cot^2A)so cot2A=(cot^2A-1)/2cotA

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