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2. If the sum of first n terms of an A.P. is 2n2 + 5n, then find its nth term.
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Answer:
Step-by-step explanation:
Sn = 2n^2 +5n
S1 =a=2(1)^2 + 5(1)
= 2+5
= 7
S2 =a+a+d = 2(2)^2 + 5(2)
= 8+10
= 18
a+a+d = S2
2a+d = 18
d = 18-2*7
d = 4
So, nth term = an = a+(n-1)d
= 7+(n-1)4
= 7+4n-4
= 3+4n
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