Question

the sum of the first n term of an AP is 3 and square + 4 and find the 25th term of this AP ​

Answer 1

Answer:

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

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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.