Sum of n terms of an ap is 2n^2+nthen 8th term is
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Sum of first n terms of AP, Sn = 2n2 + 5n Now choose n =1 and put in the above formula,First term = 2+5 = 7 Now put n=2 to get the sum of first two terms = 2x4 + 5x 2= 8 + 10 = 18 This means first term + second term = 18 but first term =7 as calculated above so, second term = 18-7 = 11 So common difference becomes, 11-7 = 4 So the AP becomes, 7, 11, 15, ....nth term = a + (n - 1)d = 7 + (n-1)4 = 7 + 4n - 4 = 3 + 4n
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