This is the basic and conceptual question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise 9.6
In this question we have been given an arithmetic progression. And we have to find its sum upto 12 terms.
CBSE DHANPAT RAI publications
Class:- 10th
Solutions of CBSE Mathematics
Question 1(ii)
Given A.P. has first term(a) = 1,
common difference(d) = 3 – 1 = 2
and number of terms(n) = 12
So, Sum of A.P. = S12 = n[2a + (n – 1)d] / 2
= 12[2(1) + (12 – 1)(2)]/2
= 12[2 + 22]/2
= 144
Hence, the sum of the first 12 terms of A.P. is 144.