Write the sum −3+5−7+9−11+13 using sigma notation. The form of your answer will depend on your choice of the lower limit of summation.?

help pls tryna get a degree.

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  • 4 weeks ago

    General term of the series can be expressed as (2r+1)*(-1)^r.

    Summation = r form 1 to 6, ∑(2r+1)(-1)^r

    • Alan
      Lv 7
      4 weeks agoReport

      They want k , so remember not use r in your answer. 

  • -3 = (-1)^1 * (1 + 1 * 2)

    5 = (-1)^2 * (1 + 2 * 2)

    -7 = (-1)^3 * (1 + 3 * 2)

    9 = (-1)^4 * (1 + 4 * 2)

    -11 = (-1)^5 * (1 + 5 * 2)

    13 = (-1)^6 * (1 + 6 * 2)

    See a pattern?  k = 0, let the function equal (-1)^k * (1 + 2k), let the last term be 6

    Or from top-down

    6

    (1 + 2k) * (-1)^k

    0

    • Alan
      Lv 7
      4 weeks agoReport

      so it is not 0 to  6 , probably just a typo 
      it is 1 to 6  

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