Question

Given that, S7 = 49 S17 = 289 S7 = 7/2 [2a + (n - 1)d] S7 = 7/2 [2a + (7 - 1)d] 49 = 7/2 [2a + 16d] 7 = (a + 3d) a + 3d = 7 ... (i) Similarly, S17 = 17/2 [2a + (17 - 1)d] 289 = 17/2 (2a + 16d) 17 = (a + 8d) a + 8d = 17 ... (ii) Subtracting equation (i) from equation (ii), 5d = 10 d = 2 From equation (i), a + 3(2) = 7 a + 6 = 7 a = 1 Sn = n/2 [2a + (n - 1)d] = n/2 [2(1) + (n - 1) × 2] = n/2 (2 + 2n - 2) = n/2 (2n) = n2

Answer 1

n square is the. right answer