Multiple Choice Question (MCQ)

Which one is the formula for the general term of the arithmetic sequence -\dfrac{1}{3},\dfrac{1}{9},-\dfrac{1}{27},\dots

  1. ×

    -\dfrac{1}{3^n}

  2. ×

    \dfrac{1}{3n^2}

  3. \dfrac{(-1)^n}{3^n}

  4. ×

    none of above

Collected in the board: Arithmetic sequence

Steven Zheng posted 11 hours ago

Answer

  1. -\dfrac{1}{3},\dfrac{1}{9},-\dfrac{1}{27},\dots

    For a_n =\dfrac{(-1)^n}{3^n}

    when n =1, a_1 = \dfrac{(-1)^1}{3^1} = -\dfrac{1}{3}

    When n = 2, a_2 = \dfrac{(-1)^2}{3^2} = \dfrac{1}{9}

    When n = 3, a_3 = \dfrac{(-1)^3}{3^3} = -\dfrac{1}{27}

    Therefore, C is the right option

Steven Zheng posted 11 hours ago

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