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      Question

      Evaluate the following: cos 40° × cos 40° +

      sin 40° × sin 40°
      B 1 Correct Answer Incorrect Answer
      C 1/2 Correct Answer Incorrect Answer
      D 1/√2 Correct Answer Incorrect Answer

      Solution

      We know that, cos (a − b) = cos a × cos b + sin a × sin b So, cos 40° × cos 40° + sin 40° × sin 40°
      = cos (40° − 40°)
      = cos 0°
      = 1

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