15 sigma n=1 (3n-10)

jawab

15
Σ  (3n -10) = S15
n= 1

un = 3n-10
a= 3-10 = -7
u15= 3(15) - 10 = 45- 10
u15 = 35

Sn = n/2 (a + un)
s15 =15/2 (-7 +35)
S15= 15/2 (28)
S15 = 210

[tex]15 \: sigma \: n = 1 \: (3n - 10) \\ (3. 1 - 10) + (3.2 - 10) + (3.3 - 10) + \\ (3.4 - 10) + (3.5 - 10) + (3.6 - 10) + \\ (3.7 - 10) + (3.8 - 10) + (3.9 - 10) + (3.10 - 10) + \\ (3.11 - 10) + (3.12 - 10) + (3.13 - 10) + (3.14 - 10) + (3.15 - 10) \\ = - 7 - 4 - 1 + 2 + 5 + 8 + 11 + 14 + 17 + 20 + 23 + 26 + 29 +32 + 35 \\ = 210[/tex]
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