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
S_{1 }= 3(1) + 2(1)^{2} = 5 = t_{1}S_{2} = 3(2) + 2(2)^{2} = 14 = t_{1} + t_{2}∴ S_{2} - S_{1} = 9 = t_{2}∴ d = t_{2} - t_{1} = 9 - 5 = 4