Find the value of $k$ if $(x + 4)(x + k) = x^{2} + 9x + 20$.

Find the value of $k$ if $(x + 4)(x + k) = x^{2} + 9x + 20$.
  1. $5$
  2. $4$
  3. $3$
  4. $9$

Solution

Identity gives $4 + k = 9$ and $4k = 20$. Both yield $k = 5$.

Asked in: IMO

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