Factorise $4x^{2} - 4x - 15$.

Factorise $4x^{2} - 4x - 15$.
  1. $(2x - 5)(2x + 3)$
  2. $(2x + 5)(2x - 3)$
  3. $(4x - 5)(x + 3)$
  4. $(4x + 5)(x - 3)$

Solution

Product $=-60$, sum $=-4$: $-10, 6$. $4x^{2}-10x+6x-15 = 2x(2x-5)+3(2x-5) = (2x-5)(2x+3)$.

Asked in: IMO

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