What is the value of cos (2tan-1 x + 2cot-1 x) ?

  1. 0
  2. 1
  3. -1
  4. None of these

Answer (Detailed Solution Below)

Option 3 : -1
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Detailed Solution

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Concept:

tan-1 x + cot-1 x = \(\rm \frac {π}{2}\)

 

Calculation:

To Find: Value of cos (2tan-1 x + 2cot-1 x)

cos (2tan-1 x + 2cot-1 x) = cos 2(tan-1 x + cot-1 x)

As we know, tan-1 x + cot-1 x = \(\rm \frac {π}{2}\)

cos (2tan-1 x + 2cot-1 x) = cos [2 × \(\rm \frac {π}{2}\) ]

= cos π 

= -1

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