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    • Question

      A sequence {Tₙ} is defined for n ≥ 1 as follows:

      I) T₁ + T₂ = 16 II) For every n ≥ 3, Tₙ = Tₙ₋₁ + Tₙ₋₂ + 2 III) T₄ = 22 What is the value of T₆?
      A 23 Correct Answer Incorrect Answer
      B 66 Correct Answer Incorrect Answer
      C 72 Correct Answer Incorrect Answer
      D 49 Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      Let T₁ = a, T₂ = b. Then: T₃ = T₂ + T₁ + 2 = a + b + 2 T₄ = T₃ + T₂ + 2 = (a + b + 2) + b + 2 = a + 2b + 4 Given T₄ = 22: a + 2b + 4 = 22 a + 2b = 18 …(1) Also T₁ + T₂ = 16: a + b = 16 …(2) Subtract (2) from (1): (a + 2b) − (a + b) = 18 − 16 b = 2 Then a = 16 − b = 16 − 2 = 14 Now: T₃ = a + b + 2 = 14 + 2 + 2 = 18 T₄ = 22 (given, consistent) T₅ = T₄ + T₃ + 2 = 22 + 18 + 2 = 42 T₆ = T₅ + T₄ + 2 = 42 + 22 + 2 = 66 So T₆ = 66.

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