Q. 7

# The first term of

Given,

a = 5, last term, l = an = 80

Common difference, d = 3

We know, an = a + (n – 1)d where a is first term or a1 and d is common difference and n is any natural number

an = 5 + (n – 1)3

an = 5 + 3n – 3

an = 3n + 2

To find total terms of the A.P., put an = 80 as 80 is last term of A.P.

3n + 2 = 80

3n = 80 – 2

3n = 78

n = 26

Hence, there are total 26 terms in the given A.P.

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