Question

Given the sequence {-1, 3, 7, 11, ...}, find a25

Answer 1

here,

a1=-1

a2=-1+4 =3

a3= 3+4=7

a4=7+4=11

using the general formula for nth term of an ap

$an = - 1 + (n - 1)d \\ here \: a = - 1 \: and \: d = 4 \\ \\ an = - 1(n - 1)(4) = - 1 + 4 - 4 \\ 4n - 5 \\ \\ hence \: a25 = \\ 4(25) - 5 = 100 - 5 = 95$

Answer= a25 = 95