If the sum of n terms of an A.P. is given by Sn = 3n + 2n2, then the common difference of the A.P. is

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asked Feb 20, 2018 in Class XI Maths by vijay Premium (527 points)

If the sum of n terms of an A.P. is given by Sn = 3n + 2n2, then the common difference of the A.P. is
(a) 3                       
(b) 2                          
(c) 6                         
(d) 4 

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1 Answer

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answered Feb 20, 2018 by rahul152 (-2,861 points)

S1 = 3(1) + 2(1)2 = 5 = t1
S2 = 3(2) + 2(2)2 = 14 = t1 + t2
∴ S2 - S1 = 9 = t2
∴ d = t2 - t1 = 9 - 5 = 4  

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