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      Question

      What is the value of

      cos75Β°?Β 
      A (√2 – 1) Correct Answer Incorrect Answer
      B (√2/4) Γ— (√3 – 1) Correct Answer Incorrect Answer
      C (√3 – 1) Correct Answer Incorrect Answer
      D (√3/6) Γ— (√3 – 1) Correct Answer Incorrect Answer

      Solution

      cos75oΒ = cos(45 + 30)o Since, cos(A + B) = cosAcosB – sinAsinB So, cos 75oΒ = cos45ocos30o – sin45osin30oΒ = {(1/√2) Γ— (√3/2) – (1/√2) Γ— (1/2)} = (√3/2√2) – (1/2√2) = (1/2√2) Γ— (√3 – 1) On multiplying both numerator and denominator by √2, we have; = (√2/4) Γ— (√3 – 1)

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