Question

If the sum of first n term of an ap is 3n square minus 2n

Answer 1

Given Sn = 3n2 + 4n S1 = 3×1 + 4×1 = 7. S2 = 3×4 + 4×2 = 12 + 8 = 20. Therfore First term a1 = 7 & Second term a2 = 20 - 7 = 13 and d = 13 - 7 = 6. Now 25th term an = 7 + ( 25 - 1) 6 a25 = 7 + 24 x 6 a25 = 151.

Answer 2

sum of n terms of an AP=3n2-2n

s1 = 3(1)2 - 2(1) = 1

s2 = 3(2)2 - 2(2) = 12 - 4 = 8

therefore the 1st term of the AP is 1 and the second term is 8-1 = 7

and the common difference 6

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