📐 Sum of First n Positive Integers

$1 + 2 + \\cdots + n = \\frac{n(n+1)}{2}$

Proof: Base case: $n=1$ gives $1 = 1(2)/2$. Induction step: Assume true for $k$. Then $1 + \\cdots + k + (k+1) = \\frac{k(k+1)}{2} + (k+1) = \\frac{(k+1)(k+2)}{2}$.

From: intro-discrete

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