Question

Find Sn for the arithmetic series 14+10+6 + … and determine the value of n for which: Sn = −18. What does n = to? Sn = ? S? = -18

Answer 1

Answer:

given that

Sn=-18,a=14,d= -4

n=?

so formula

Sn=n/2(2a+(n-1).d)

-18=n/2(2×14+(n-1).×(-4)

-18=n/2(28+(n-1)×(-4))

-18=n/2 ×(-4) (-7+n-1)

36=n×4(n-8)

9=n^2-8n

n^2-8n-9=0

n^2-9n+n-9=0

(n-9).(n+1)=0

n=9, -1 Ans

Step-by-step explanation:

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