1.

Find the indicated terms in each of the following arithmetic progression:a = 21, d = -5; tn, t25

Answer»

Given: a = 21 , d = –5

To find: tn and t25

We have,

tn = a + (n – 1)d

tn = 21 + (n – 1)(–5)

= 21 – 5n + 5

tn = 26 – 5n

Now, n = 25

So, t25 = 21 + (25 – 1)(–5)

= 21 + 24 × (–5)

t25 = 21 – 120

t25 = –99



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