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Question 6. Find the sum of first 20 terms the sequence whose nth term is an = An + B.

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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


1 Answer

  1. 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.

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