Question 616825
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Hi,Previously Posted
 use partial sum formulas and the information provided to find the sum :
1 - 4 + 16 - 64 .... n = 9   Geometric {{{a[1]}}} = 1 and r = -4
  {{{sum( a[n], n=1, n ) = a[1]((1-r^n)/(1-r))}}}
  {{{sum( 1*(-4)^(n-1), n=1, 9 ) = 1*((1-(-4)^9)/(5)) =highlight(52429)}}}
20 + 27 + 34 + 41 .... n = 16  Arithmetic {{{a[1]}}} = 20 and d = 7
{{{S[n]=(n/2)(2*a[1]+ (n-1)d)}}}
{{{S[16]=(16/2)(2*20+ (15)7)= highlight(1160)}}}