Question 481797
  <pre><font face = "Tohoma" size = 4 color = "indigo"><b> 
Hi,
geometric sequence
{{{a[n]=a[1]r^(n-1)}}}
{{{b[3]=a[1]r^2= 9}}}  {{{a[1]}}} = 9/r^2
{{{b[6]=a[1]r^5= -64/3)}}}
         {{{(9/r^2)r^5 = (-64/3)}}}
                   r^3 = -64/27 
                     r= -4/3   and {{{a[1]= 9/(-4/3)^2 = 81/16}}}
{{{s[n]=a1*(1-r^n)/(1-r)}}} 
  {{{s[6]= (81/16)*(1-(-4/3)^6)/(7/3)}}}