Question 913253
{{{S[an]= (n(a[1]+a[n]))/2 }}}
{{{S[bn]= (n(b[1]+b[n]))/2 }}}
{{{((n(a[1]+a[n]))/2)/((n(b[1]+b[n]))/2)  =(a[1]+a[n])/ (b[1]+b[n]) = (13-7n)/(3n+1)}}}
{{{(a[1]+a[n])/ (b[1]+b[n]) = (13-7n)/(3n+1)}}}
n = 1
{{{2a[1]/2b[1] = 6/4}}} , {{{a[1]/b[1] = 3/2}}}
n = 2
{{{(a[1]+a[2]) / (b[1]+b[2]) = (3/2 + (a[2]/b[1] ))/(1 + (b[2]/b[1] )) = (-1)/7}}}     
{{{a[2]/b[2] = (-5/2)/6 }}}