Question 631826
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
sum of the arithmetic sequence 2, 4, 6, 8, ..., 70. 
to Apply**** {{{S[n]=(n/2)(2*a[1]+ (n-1)d)}}}
I. determine d= 2 and n = 35 |note:  70 = {{{2  +(n-1)*2}}} as {{{a[n]=a[1]+(n-1)*d}}}
II. Substitute values found into {{{S[n]=(n/2)(2*a[1]+ (n-1)d)}}} to find Sum requested
{{{S[35]=(35/2)(2*2+ (34)2)}}}  Do calculation
14, 8, 2,...; n=9  same as above Steps
{{{S[9]=(9/2)(2*14+ (8)(-6))}}}

sum of the geometric sequence -1, 11, -121, ...; n = 9 
to Apply****{{{S[n] = a[1]((1-r^n)/(1-r))}}}
I.  determine r and n
II.  Substitute into Formula
Recommend Posting the Geomteric Sequences separately