The correct option is D (a−2)(a+1)(4a2−4a+3)
(a2−a)(4a2−4a−5)−6
=(a2−a)[4(a2−a)−5]−6
Let (a2−a)=x
Thus,
x(4x−5)−6
=4x2−5x−6
=4x2−8x+3x−6
=4x(x−2)+3(x−2)
=(x−2)(4x+3)
Putting the value of x
=(a2−a−2)[4(a2−a)+3]
=(a2−2a+a−2)(4a2−4a+3)
=(a(a−2)+1(a−2))(4a2−4a+3)
=(a−2)(a+1)(4a2−4a+3)