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If Sn is the sum of the first n terms of a certain sequence and if Sn = n(n+1) for all positive integers n, what is the third term of the sequence?
Option C is the correct answer.
Let there be 3 terms in the sequence, namely a, b & c
Given that a + b + c = 3 * 4 = 12………….. (1)
Now say there are 2 terms, namely a & b
So, a + b = 2 * 3 = 6………. (2)
Substitute value of a+b from eqn (2) in eqn (1)
6 + c = 12
c = 6