Question 1047523
a.  {{{a[6] = -0.1875}}}, {{{a[7] = 0.09375}}}, with r = -1/2.


b.  {{{a[n] = a[1]*r^(n-1) = 6*(-1/2)^(n-1)}}}


c.  {{{S[n] = 6*((1-(-1/2)^n)/(1-(-1/2))) = 4*(1-(-1/2)^n)}}}.