`a, = (x-y)(x+y) - (x-y) = (x+y-1)(x-y)`
`b, = (x-2)(x+2) - 2(x-2)^2`
`= (x-2)(6 - x)`
`c, = (x-y)(x+y) - 2(x+y)`
`= (x-y-2)(x+y)`
`d, (1-x^2)(x^2-9)`
`= (1-x)(1+x)(x-3)(x+3)`
`e, = (2x -y)(4x^2 + 2xy + y) - 2(2x-y)`
`= (2x-y)(4x^2 + 2xy + y -2)`
`f, (x+y)(x^2+xy+y^2) - 2(x+y)`
`= (x+y)(x^2+xy+y^2 - 2)`
5: \(=\left(x-y\right)\left(x+y\right)-\left(x-y\right)\)
\(=\left(x-y\right)\left(x+y-1\right)\)
6: \(=\left(x-2\right)\left(x+2\right)-2\left(x-2\right)^2\)
\(=\left(x-2\right)\left(x+2-2x+4\right)\)
\(=\left(x-2\right)\left(-x+6\right)\)
7: \(=\left(x-y\right)\left(x+y\right)-2\left(x+y\right)=\left(x+y\right)\left(x-y-2\right)\)
9" \(=\left(2x-y\right)\left(4x^2+2xy+y^2\right)-2\left(2x-y\right)\)
\(=\left(2x-y\right)\left(4x^2+2xy+y^2-2\right)\)
