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0 votes
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in Arithmetic Progression by (30.9k 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

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by (31.3k points)
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Best answer

Correct answer is C. 4n + 3

Here Sn = 2n2 + 5n 

Sum of the A.P with 1 term = S1 = 2 + 5 = 7 = first term 

Sum of the A.P with 2 terms = 8 + 10 = 18 

Sum of the A.P with 3 terms = 18 + 15 = 33 

a2 = S2 – S1 = 18 – 7 = 11 

d = a2 –a1 = 11 – 7 = 4 

nth term = a + (n–1) d 

= 7 + (n–1) 4 

nth term = 4n + 3

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