Find the sum of :(i)         the first 1000 positive integers(ii)        the first n positive integers

Explanation

1)a=1 and d=1

`S_n=n/2(a+l)`

`S_n=1000/2(1+1000)`

`S_n=500(1001)`

`S_n=500500`

2) a=1 and d=1

`S_n=n/2(a+n)`

`S_n=n/2(1+n)`

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