Q. 113.8( 4 Votes )

Find the rth term of the AP, the sum of whose first n terms is (3n2 + 2n).

Answer :

Given: The sum of first n terms.


To Find: The rth term.


Let the first term be a and common difference be d


Put n = 1 to get the first term
a = S1 = 3 + 2 = 5
Put n = 2 to get a + (a + d)
2a + d = 12 + 4 = 16
10 + d = 16
d = 6
tr = a + (r - 1)d
t �r = 5 + (r - 1)6 = 5 + 6r - 6 = 6r - 1


The rth term is given by 6r - 1.


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