mtayab1994
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Homework Statement
1+2+3...+n
Homework Equations
count the sum.
The Attempt at a Solution
it's such an easy sum to count but i just want to make sure.
S_{n}=\frac{n}{2}(a_{1}+a_{n})
S_{n}=\frac{n}{2}(1+n)
S_{n}=\frac{n+n^{2}}{2}