Question 448470
  <pre><font face = "Tohoma" size = 4 color = "indigo"><b> 
Hi,
Arithmetic series/7 terms: {-13,-16,-19,...} {{{highlight(d=-3)}}}
{{{S[n]=(n/2)(2*a[1]+ (n-1)d)}}}
{{{S[7]=(7/2)(2*-13+ 6*-3) = highlight(-154)}}}