Q57 / 150 · MHT CET 2016 · Mathematics

If 2tan-1⁡cos⁡x=tan-1⁡(2cosce⁡x) then sin⁡x+cos⁡x=

  • A
    22
  • Correct answer
    B
    2
  • C
    12
  • D
    12

Solution

As given, 2tan-1⁡ cos⁡ x=tan-1⁡ (2cosce⁡ x)
tan-1⁡ cos⁡ x+tan-1⁡ cos⁡ x=tan-1⁡ (2cosce⁡ x)
Since cos x ≤ 1
=tan-1⁡ 2cos⁡ x1-cos2⁡ x=tan-1⁡ (2cosce⁡ x)
⇒  2cos⁡ xsin2⁡ x=2cosce⁡ x
⇒ 2cot⁡ x=2
⇒ cot⁡ x=1
⇒ x=π4
Hence,
sin⁡ x+cos⁡ x=sin⁡π4+cos⁡π4
=12+12
=2

Hence, the correct answer is option: 'B'.

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