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  • If the sum of n terms of an A.P. is given by Sn = 3n + 2n 2, then the common difference of the A.P. is (A) 3 (B) 2 (C) 6 (D) 4

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

(A) 3 (B) 2 (C) 6 (D) 4

Answers (1)

Given that S_{n}=3n+2n^{2}

We know that  a_{2}=S_{2}-S_{1}

 \\ = \left( 3 \left( 2 \right) +2 \left( 2 \right) ^{2} \right) - \left( 3 \left( 1 \right) +2 \left( 1 \right) ^{2} \right) \\\\ =14-5 \\\\ =9 \\\\ a_{1}=S_{1}=3 \left( 1 \right) +2 \left( 1 \right) ^{2}=5 \\\\ d=a_{2}-a_{1}=9-5=4 \\\\

Hence, correct option is d.

Posted by

infoexpert21

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