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 whose nth term is given by an=2-3n. And we have to find out sum of this progression of first 25 terms
CBSE DHANPAT RAI publication
CBSE Mathematics Class 10th
Question 7
Given A.P. has nth term, an = 2 – 3n
and number of terms(n) = 25
So, an = 2 – 3(25) = -73
On putting n = 1, we get a, first term of the A.P.,
a = 2 – 3(1) = -1
S20 = n[a + an]/2
= 25(-1 – 73)/2
= 25 x (-37) = -925
Hence, the sum of the first 25 terms of given A.P. is -925.