Question

If the nth term of an A.P. -1, 4, 9, 14,..... is 129. Find the value of n and Sn​

Answer 1

Answer:

Hope it help mate !!!

Please mark me Brainliest.

Answer 2

AP : –1, 4, 9, 14, ..., 129

So, Tn = (–1) + (n–1)(5)

= –1 + 5n –5

= 5n – 6

For, Tn = 129 = 5n–6

n = 27

Here, Sn = n/2 (T1+Tn) = n/2(Tn – 1)

= 27/2 (–1+129)

= 27 (64)

S_(27) = 1728