Question

How many terms of the AP 1,9,17...must be taken to give a sum of 1540

Answer 1

Answer:

a=1

d=8

s=1540

n=???

$s = \frac{n}{2} \times [2a + (n - 1)d] \\ \rightarrow 1540 = \frac{n}{2} \times [2(1) + (n - 1)(8)] \\ \rightarrow3080 = n[2 + 8n - 8] \\ \rightarrow3080 = {8n}^{2} - 6 n \\ \rightarrow2(1540) = 2(4 {n}^{2} - 3n) \\ \rightarrow4 {n}^{2} - 3n - 1540 = 0$

solve this equation, u will get ur answer

hope it helps you....✌✌