This is an arithmetic progression based question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise – 9.6
In this question we have been given the arithmetic progression. Also we have to find the sum of its first 13 terms.
CBSE DHANPAT RAI PUBLICATIONS
Understanding CBSE Mathematics
Class :- 10th
Question no 11(ii)
Given A.P. has first term(a) = -6,
Common difference(d) = 0 − (−6) = 6
and number of terms(n) = 13.
We know sum of n terms of an A.P. is given by, Sn = n[2a + (n − 1)d] / 2.
S13 = 13[2(−6) + (13 − 1)6]/2
= 13[(−12) + 72]/2
= 13[30] = 390
Hence, the sum of first 13 terms of the given A.P. is 390.