mhacangelo
mhacangelo mhacangelo
  • 24-09-2021
  • Mathematics
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Find S25 for the sequence -8, 7, …15n-23

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ItzUrChinkiMinki
ItzUrChinkiMinki ItzUrChinkiMinki
  • 24-09-2021

Answer:

For an arithmetic series (note: the sum of the terms in an arithmetic sequence), the formula is:

Sn = ( 2a1 + (n-1)d ) * n/2

Plug in the values of:

n=25

a1 = -4

d = 3

S25 = ( 2*(-4) + (25-1)(3))*(25/2)

S25 = (-8 + 72)*25/2

S25 = (64)(25/2)

S25 = 800

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