Question

factorise : (x^2-4x) (x^2- 4x-1) - 20

Answer 1

(x² - 4x )(x² -4x -1) -20 

let (x² -4x ) = P 


P(P -1) -20 

P² -P -20

P² -5P +4P -20

P( P -5) +4 ( P -5) 

(P +4 )( P -5) 

put P = x² - 4x 

(x² -4x +4)( x² - 4x -5)

(x -2)²( x + 1)(x -5)

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