Expand $(x - 5)^{2}$.

Expand $(x - 5)^{2}$.
  1. $x^{2} - 10x + 25$
  2. $x^{2} - 5x + 25$
  3. $x^{2} + 10x + 25$
  4. $x^{2} - 25$

Solution

$(a-b)^{2} = a^{2} - 2ab + b^{2}$ with $a = x,\ b = 5$: $x^{2} - 10x + 25$.

Asked in: IMO

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