nakworm01
nakworm01 nakworm01
  • 16-04-2015
  • Mathematics
contestada

Find sum of -3,2,7,12....,132
Arithmetic series

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naǫ
naǫ naǫ
  • 16-04-2015
[tex]a_1=-3 \\ d=2-(-3)=5 \\ a_n=132 \\ \\ a_n=a_1+d(n-1) \\ 132=-3+5(n-1) \\ 132=-3+5n-5 \\ 132=-8+5n \\ 140=5n \\ n=28 \\ \\ S_n=\frac{n(a_1+a_n)}{2} \\ S_{28}=\frac{28(-3+132)}{2}=\frac{28 \times129}{2}=14 \times 129=1806[/tex]

The sum is 1806.
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