`a)x^3-6x^2+9x-4xy^2`
`=x(x^2-6x+9-4y^2)`
`=x[(x-3)^2-4y^2]`
`=x(x-3-2y)(x-3+2y)`
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`b)x^2-4xy+3x-12y`
`=x(x-4y)+3(x-4y)`
`=(x-4y)(x+3)`
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`c)5x^2+17x+6`
`=5x^2+15x+2x+6`
`=5x(x+3)+2(x+3)`
`=(x+3)(5x+2)`