How many terms of the series -8,-6,-4 amount of 70?

1.	How many terms of the series -8,-6,-4 amount of 70?
Answer» Answer: 14 Step-by-step explanation: a = -8 d = 2 Sn = 70 Sn = N/2[2a+(n-1)d] 70 = n/2[2(-8) + (n-1)2] 70 = n(-8 + n - 1) 70 = n(n -9) n^2 -9N -70 = 0 n^2+5n-14n-70 = 0 n(n+5)-14(n+5) = 0 (n+5)(n-14) = 0 n = 14 & -5 Since terms will be positive n = 14

Answer»

Answer:

Step-by-step explanation:

a = -8

d = 2

Sn = 70

Sn = N/2[2a+(n-1)d]

70 = n/2[2(-8) + (n-1)2]

70 = n(-8 + n - 1)

70 = n(n -9)

n^2 -9N -70 = 0

n^2+5n-14n-70 = 0

n(n+5)-14(n+5) = 0

(n+5)(n-14) = 0

n = 14 & -5

Since terms will be positive n = 14

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How many terms of the series -8,-6,-4 amount of 70?

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