One of the most important and exam oriented question from Chapter name- Arithmetic Progression
Class 10th
Chapter number- 9
Exercise :- 9.6
This type of question has been asked in previous years exams.
In this question we have been given an arithmetic progression. And we have to find out sum of this progression.
CBSE DHANPAT RAI publication
CBSE Mathematics Class 10th
Question 13(iii)
Given series is an A.P. with first term(a) = -5,
Common difference(d) = (−8) − (−5) = −3 and nth term(an) = −230.
We know nth term of an A.P. is given by, an = a + (n − 1)d.
=> −230 = −5 + (n − 1)(−3)
=> −230 = −5 − 3n + 3
=> n = 228/3
=> n = 76
Also we know sum of n terms of an A.P. is given by Sn = n[a + an]/2.
S76 = 76 [−5 + (−230)]/2
= 38 x (−235) = −8930
Hence, the sum of terms of the given series is –8930.