a, x3 - x2 - x + 1
= x\(^2\) ( x - 1 ) - (x - 1 )
= ( x\(^2\) - 1 ) (x - 1 )
b, x2y2 + 1 - x2 - y2
= ( \(x^2y^2\) - \(x^2\) ) - ( \(y^2\) - 1 )
= \(x^2\) ( \(y^2-1\)) - ( \(y^2-1\) )
= ( \(x^2-1)\left(y^2-1\right)\)
c, x4 - x2 + 2x - 1
= \(x^4\) - (\(x^2\) - 2x + 1 )
= (x\(^2\))\(^2\) - (x - 1 )\(^2\)
= ( x\(^2\) - x + 1 ) (x\(^2\) + x -1 )
e, x2 - y2 - 2x - 2y
= (x - y ) ( x + y ) - 2 ( x + y )
= ( x - y - 2 ) ( x+ y )
f, x2 - y2 + 2y - 1
= x\(^2\) - ( y\(^2\) - 2y + 1 )
= x\(^2\) - ( y - 1 )\(^2\)
= (x - y +1 ) ( x+y - 1)