Q. 254.0( 7 Votes )

# Find the sum of first 20 terms of these sequence whose n^{th} term is .

Answer :

Given, a_{n}= An + B

Put n = 1, a_{1}= A + B

Put n = 20, a_{20}= 20A + B

S_{20}= [a + l]

= 10 [A + B + 20A + B]

= 10 [21A + 2B]

= 210A + 20B

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