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    • Question

      If sec(2A + B) = 2 and cos(A + B) = (1/√2) , find the

      value of {sec 2B + tan (A + B) } given that 0o < A, B < 90o
      A 4 Correct Answer Incorrect Answer
      B 2 Correct Answer Incorrect Answer
      C 1 Correct Answer Incorrect Answer
      D 3 Correct Answer Incorrect Answer

      Solution

      We have, sec(2A + B) = 2

      Or, sec(2A + B) = sec 60o

      Or, 2A + B = 60o -------- (I)

      And, cos(A + B) = (1/√2)

      Or, cos(A + B) = cos 45o

      Or, A + B = 45o ------- (II)

      On subtracting equation (II) from (I) ,

      We have, (2A + B) - (A + B) = 60o - 45o

      Or, 'A' = 15o

      Put the value of 'A' = 15o in equation (1) ,

      So, 2 X 15o + B = 60o

      Or, 30o + B = 60o

      Or, 'B' = 30o

      Therefore, required value = sec (2 X 30o) + tan (15o+30o)

      = sec 60o + tan 45o = 2 + 1 = 3

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