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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