Tylerpinkston Tylerpinkston
  • 18-10-2016
  • Mathematics
contestada

what is the sum of the last four terms of the series 7+9+11+...21

Respuesta :

SJ2006
SJ2006 SJ2006
  • 18-10-2016

For sake of convenience, reverse the series, then it would be:

21,19,17.....7

a=21, d = -2,

s(4) = 4/2 (21+15)

s(4)=2(36)

s(4) = 72


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