Factorise $49x^{2} - 28xy + 4y^{2}$.

Factorise $49x^{2} - 28xy + 4y^{2}$.
  1. $(7x - 2y)^{2}$
  2. $(7x + 2y)^{2}$
  3. $(7x - 2y)(7x + 2y)$
  4. $(7x - 4y)(7x - y)$

Solution

$49x^{2}-28xy+4y^{2} = (7x)^{2} - 2 \cdot 7x \cdot 2y + (2y)^{2} = (7x-2y)^{2}$.

Asked in: IMO

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