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      Question

      If cos 2A = 15, then find cos

      A
      A √8 Correct Answer Incorrect Answer
      B 2√2 Correct Answer Incorrect Answer
      C √6 Correct Answer Incorrect Answer
      D 4 Correct Answer Incorrect Answer

      Solution

      We know, cos 2X = 2cos² X − 1 So, 2cos² A − 1 = 15 Or, 2cos² A = 16 Or, cos² A = 8 Or, cos A = √8

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