Question

Factories:
$({ x}^{2} - 4x)( {x}^{2} - 4x - 1) - 20$
​

Answer 1

Answer:

$( {x}^{2} - 4x) ( {x }^{2} - 4x - 1) - 20 \\ let \: {x}^{2} - 4x = a \\ a(a - 1) - 20 \\ {a }^{2} - a - 20 \\ {a}^{2} - 5a + 4a - 20 \\ a(a - 5) + 4(a - 5) \\( a - 5) \: (a + 4)$