Factorise $x^{2} + x - 12$.

Factorise $x^{2} + x - 12$.
  1. $(x + 4)(x - 3)$
  2. $(x - 4)(x + 3)$
  3. $(x + 6)(x - 2)$
  4. $(x + 12)(x - 1)$

Solution

Need $a+b=1, ab=-12$: $a=4, b=-3$. So $(x+4)(x-3)$.

Asked in: IMO

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