$1 + 3 + 5 + \ldots + (2n - 1)$ equals

$1 + 3 + 5 + \ldots + (2n - 1)$ equals
  1. $n^{2}$
  2. $\dfrac{n(n+1)}{2}$
  3. $n^{3}$
  4. $2n$

Solution

Standard identity: the sum of the first $n$ odd numbers equals $n^{2}$.

Asked in: IMO

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