Question

add 17 term of series 5+1-3...​

Answer 1

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