`x^3+x^2+4`
`= x^3 + 2x^2 - x^2 + 4`
`= x^2(x+2)+4-x^2`
`= x^2(x+2)+(2-x)(2+x)`
`= (x+2)(x^2+2-x)`
............................................
`2x^3-5x^2+8x-3`
`= 2x^3 - x^2 - 4x^2 + 2x + 6x - 3`
`= x^2(2x-1)-2x(2x-1)+3(2x-1)`
`= (2x-1)(x^2-2x+3)`
.............................................
`3x^3-7x^2+17x-5`
`= 3x^2-x^2-6x^2+2x+15x-5`
`= x^2(3x-1)-2x(3x-1)+5(3x-1)`
`= (3x-1)(x^2-2x+5)`
