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= 3+4n. And we have to find out sum of this progression of first 15 terms.
CBSE DHANPAT RAI publication
CBSE Mathematics Class 10th
Question 5(i)
Given A.P. has nth term, an = 3 + 4n
and number of terms(n) = 15
So, an = 3 + 4(15) = 63
On putting n = 1, we get a, first term of the A.P.,
a = 3 + 4(1) = 7
S15 = n[a + an]/2
= 15(7 + 63)/2 = 15 x 35 = 525
Hence, the sum of the first 15 terms of given A.P. is 525.