Given the finite arithmetic sequence: 5; 1; -3; ...; -83; -87
  1. 2.1
    Write down the fourth term (T4) of the sequence.
    (1)
    1. 2.2
      Calculate the number of terms in this sequence
      (3)
      1. 2.3
        Calculate the sum of all the negative numbers in the sequence
        (3)
        1. 2.4
          Consider the sequence: 5; 1; -3; ... ; -83 ; -87; ...; -4187
          Determine the number of terms in this sequence that will be exactly divisible by 5.
          (4)
          (11)
          [{"prnt":"2","num":"2.1","answer":""},{"prnt":"2","num":"2.2","answer":""},{"prnt":"2","num":"2.3","answer":""},{"prnt":"2","num":"2.4","answer":""}]

          Answers

            1. 2.1
              d = -4
              T4 = -7
              1. 2.2
                Tn = a + (n-1)d = 5 - 4n + 4 = 9 - 4n

                Thus, -87 = 9 - 4n
                n = 24
                1. 2.3
                  -3; -7; ...; -87

                  Sn = n2[2a + (n-1)d]
                  S22 = 222[2(-3) + (22-1)(-4)]
                  = -990
                  1. 2.4
                    5; -15; -35;...
                    d = -20
                    Tn = 25 - 20n
                    -4187 = 25 - 20n
                    n = 210
                    Msaki, 24 Mar 2018 11:59
                    1. 2.1
                    2. 2.2
                    3. 2.3
                    4. 2.4
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