`\text{a)} 5x^3 - 10x^2y + 15x^2`
`= 5x^2 (x - 2y + 3)`
`\text{b)} x^3y^2 - 6x^2y^2 + x^3y^3`
`= x^2y^2 (x - 6 + xy)`
`\text{c)} 5x - xy + 5y - y^2`
`= x(5 - y) + y(5 - y)`
`= (5 - y)(x + y)`
`\text{d)} x^2 - 16`
`= x^2 - 4^2`
`= (x - 4)(x + 4)`
`\text{e)} x^2 + 4x - 4`
`= - (x^2 - 4x + 4)`
`= - (x^2 - 2.x.2 + 2^2)`
`= - (x - 2)^2`
`\text{f)} x^3 - 8y^3`
`= x^3 - (2y)^3`
`= (x - 2y)(x^2 + 2xy + 4y^2)`
