Question

Find the indicated terms in each of the following arithmetic progression:

a = 21, d = -5; t_n, t₂₅

Answer 1

Given: a = 21 , d = –5

To find: t_n and t₂₅

We have,

t_n = a + (n – 1)d

t_n = 21 + (n – 1)(–5)

= 21 – 5n + 5

t_n = 26 – 5n

Now, n = 25

So, t₂₅ = 21 + (25 – 1)(–5)

= 21 + 24 × (–5)

t₂₅ = 21 – 120

t₂₅ = –99