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