Part (1),
x3−x2+x−1
=x2(x−1)+1(x−1)
=(x−1)(x2+1)
Part (2),
4x2−y2−8yz−16xz
=(2x)2−y2−8yz−16xz
=(2x+y)(2x−y)−8z(y+2x)
=(2x+y)(2x−y−8z)
Hence, this is the answer.