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If the sum of the first 9 terms of an AP is equal to sum of the first 11 terms, then what is the sum of the first 20 terms?

Options

  1. A20
  2. B10
  3. C2
  4. D0

Correct answer

D. 0

Step-by-step solution

According to questions aligned & S ₉= S ₁₁ & 9 2 (2 a +8 ~d )= 11 2 (2 a +10 ~d ) & 18 a +72 ~d =22 a +110 ~d & 4 a +38 ~d =0 2 a +19 ~d =0 & ~S ₂₀= 20 2 (2 a +19 ~d )=0 aligned

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