Question

find the sum of :first n positive integer. It is related to A.P

Answer 1

S = n/2 {2a + (n-1) d } or  n/2(l + a) where l is teh last positive integer

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Answer 2

Sum of first n positive integers =
1,2,3----------,n terms
Hence a=1
D=1
Now the formula for sum of terms in ap
$\frac{n}{2} (a + n) \\ \frac{n}{2} (first \: term + last \: term)$
now a=1
so sum =
$\frac{n}{2} (n + 1)$
So sum of first n positive integers is
$\frac{n}{2} (n + 1)$