Question

What is n in the sequence 15,7,-1,-9,-17

Answer 1

There are only five terms given so the n is 5.

Or

According to the equation of A.P.

an = a+(n-1)d

Here, a = 15

d = a2-a1, = 7-15

= -8

an = -17

Putting value , we get

-17 = 15+(n-1)×(-8)

-17 - 15 = -8n+8

-32 = -8n+8

-32-8 = -8n

-40 = -8n

-8n = -40

n = -40/-8

n = 5

Therefore, value of n in sequence = 5