An Important question based on Arithmetic progression Chapter of R.S Aggarwal book for ICSE & CBSE Board.

Here you have to find the sum of first nth terms.

This is the Question Number 1 Exercise 11 C of RS Aggarwal Solution.

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# Find the sum of first 19 terms of the AP 2, 7, 12, 17,…..

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Given:

n = 19 a = 2 d = 7-2 = 5

To find the last last term substitute given value in the following equation:

Tn = a + ( n- 1) d

= 2 + ( 19 -1 ) 5

= 2 + 18 ×5

= 2 + 90

Tn = 92

Given:

l = Tn = 92 n = 19 a =2

To get the sum of those terms in the sequence substitute the given values in the following equation:

Sn=n/2(a+l)

= 19/2(2 + 92)

= 19/2 (94)

= 19×47

Sn = 893