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 having nth term as an=An+B . And we have to find out sum of this progression of first 20 terms.
CBSE DHANPAT RAI publication
CBSE Mathematics Class 10th
Question 6
Given A.P. has nth term, an = An + B
and number of terms(n) = 20
So, an = A(20) + B = 20A + B
On putting n = 1, we get a, first term of the A.P.,
a = A(1) + B = A + B
S20 = n[a + an]/2
= 20(A+B + 20A + B)/2
= 10[21A + 2B]
= 210A + 20B
Hence, the sum of the first 20 terms of given A.P. is 210A + 20B.