`a) 15x^2-10xy+5=5(x^2-2xy+1)`
`b) 2x^2-5x=x(2x-5)`
`c) x^2-4y^2=(x-2y)(x+2y)`
`d) x^2+2xy-16+y^2=(x^2+2xy+y^2)-16`
`=(x+y)^2-4^2=(x+y+4)(x+y-4)`
`e) x^2-5x+xy-5y=x(x-5)+y(x-5)=(x-5)(x+y)`
`f) x^3-3x^2-4x+12=x^2(x-3)-4(x-3)`
`=(x-3)(x^2-4)=(x-3)(x-2)(x+2)`
`g) x^3+y^3+z^3-3xyz`
`=(x+y)^3+z^3-3xy(x+y)-3xyz`
`=(x+y+z)[(x+y)^2-(x+y)z+z^2]-3xy(x+y+z)`
`=(x+y+z)(x^2+y^2+z^2+2xy-xz-yz-3xy)`
`=(x+y+z)(x^2+y^2+z^2-xy-yz-zx)`
`h) x^2-xy-3x+3y`
`=x(x-y)-3(x-y)`
`=(x-y)(x-3)`
`i) 4x^2-y^2+2y-1`
`=4x^2-(y^2-2y+1)`
`=(2x)^2-(y-1)^2`
`=(2x-y+1)(2x+y-1)`