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in Arithmetic Progression by (24.8k points)
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If the sum of n terms of an A.P. is 2n2 + 5n , then its nth term is :

A. 4n − 3 

B. 3n − 4 

C. 4n + 3 

D. 3n + 4

1 Answer

+1 vote
by (27.0k points)
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Best answer

Option : (C)

Here, 

Sn = 2n2+5n 

∴ S1 = 2+5 = 7 

∴ a1 = S1 = 7 

And S2 = 2×2 2+5×2 = 18 

Now,

a2 = S2 - S1 

= 18-7 

= 11 

∴ d = a2-a1

= 11-7

= 4 

Now, 

an = a1+(n-1)d 

= 7+(n-1)4 

= 7+4n-4 

= 4n+3

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