-100 - 99 - 98 - ... -2 - 1 - 0 + 1 + 2 + ... + 48 + 49 + 50 *sama penjelasannya ya

a = -100
b = 1
Un = a + (n-1)b
      = -100 + n - 1
      = n - 101

50 = n - 101
n = 151

Sn = n/2 (a + Un)
S151 = 151/2 ((-100) + 50)
        = 151/2 (-50)
        = - 3.775