Factorise $x^{2} - 13x + 42$.

Factorise $x^{2} - 13x + 42$.
  1. $(x - 6)(x - 7)$
  2. $(x + 6)(x + 7)$
  3. $(x - 14)(x - 3)$
  4. $(x - 21)(x - 2)$

Solution

Need $a+b=-13, ab=42$: $a=-6,b=-7$. So $(x-6)(x-7)$.

Asked in: IMO

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