Expand $(x + 7)^{2}$.

Expand $(x + 7)^{2}$.
  1. $x^{2} + 14x + 49$
  2. $x^{2} + 7x + 49$
  3. $x^{2} - 14x + 49$
  4. $x^{2} + 49$

Solution

Use $(a+b)^{2} = a^{2} + 2ab + b^{2}$ with $a = x,\ b = 7$: $x^{2} + 14x + 49$.

Asked in: IMO

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