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    • Question

      If cosec [180° − (3q/2) ] = √2, 0° < q < 90°, then

      find the value of {(2/√3) X cos q - 4 cos 3q}.
      A √3/2 Correct Answer Incorrect Answer
      C 2 Correct Answer Incorrect Answer
      D 1 Correct Answer Incorrect Answer

      Solution

      cosec [180° − (3q/2) ] = √2

      Or, cosec (3q/2) = cosec 45 o  [because cosec 45 o  = √2, and cosec (180 - q) = cosec q]

      Or, (3q/2) = 45 o

      Or, q = 45 o  X (2/3)

      So, q = 30 o

      (2/√3) cos q - 4 cos 3q = (2/√3) cos 30 o  - 4 cos (3 X 30 o )

      = (2/√3) X (√3/2) - 0 (because, cos 30 o  = (√3/2) and cos 90 o  = 0)

      = 1

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