Question 662130
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Hi,
express given sums in summation notation: 11+15+19+23+...+71
Arithemetic Sequence:  d = 4
{{{a[n] = 11 + (n-1)d = 71}}} 
  11 + (n-1)4 = 71
    4n - 4 = 60
         n = 16
{{{a[n] = 11 + (n-1)4 =  4n + 7}}} 
11+15+19+23+...+71 is {{{sum( 4n+7, n=1, 16 )}}}