Arithmetic progression

Mathematics (NDA)

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If 1.3 + 2. 3² + 3. 3³ +.... +n. 3ⁿ = (2n−1)3^a+b / 4 then a and b are respectively-

n , 2

n , 3

n + 1 , 2

n + 1 , 3

Explanation:

1.3 +2.3² + 3.3³ +……..+ n.3ⁿ

Sn = (2n−1)3ⁿ⁺¹+3 / 4

Comparing with, (2n−1)3^a+b / 4

a = n+1, b = 3

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