add 17 term of series 5+1-3...
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Step-by-step explanation:
5+1-3......
a = 5
d = a2 - a1. ; d = a3 - a2
= 1-5 = - 4 --> (1). ; = - 3-1 = - 4 --> (2)
From 1 & 2,
d is equal. So series is in AP.
a = 5, d= - 4, n=17
Sn = n/2 [2a+(n-1)d]
S17 = 17/2 [2(5)+(17-1)-4]
S17= 17/2 [10 + 16(-4)]
S17 = 17/2[10-64]
S17 = 17/2 [-54]
S17 = 17(-54) / 2
S17 = 17 (-27)
S17 = - 459
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