Anyone knows this ?

So find the terms of the series

- A1 = 1 - 1 = 0
- A2 = 1 + 1 = 2
- A3 = 1 - 1 = 0

… and so on. Now let’s find the pattern in the sums

- S1 = A1 = 0
- S2 = A1 + A2 = 2
- S3 = A1 + A2 + A3 = 2
- S4 = A1 + A2 + A3 + A4 = 4
- S5 = A1 + A2 + A3 + A4 + A5 = 4

… and so on. As you can see, sum of the first n odd numbers is nothing but the sum before it. And sum of the first n even numbers is n itself. So S39 will be the same as S38 which is 38 itself. So Quantity A will be 38

1 Like