`a)`
`2x^4 + 3x^3 - 9x^2 -3x + 2`
`= (2x^4 + 5x^3 - 2x^2) - (2x^3 + 5x^2 - 2x) - (2x^2 + 5x -2)`
` = x^2 (2x^2 + 5x - 2) - x (2x^2 + 5x - 2) - (2x^2 + 5x - 2)`
` = (x^2 - x - 1)(2x^2 + 5x -2)`
`b)`
`x^4 - x^3 - 10x^2 + 2x + 4`
` = (x^4 + 2x^3 - 2x^2) - (3x^3 + 6x^2 - 6x) - (2x^2 + 4x - 4)`
` = x^2 (x^2 + 2x - 2) - 3x (x^2 + 2x - 2) - 2 (x^2 + 2x - 2)`
`= (x^2 - 3x-2)(x^2 + 2x - 2)`
`c)`
`x^4 - 3x^3 - 6x^2 + 3x + 1`
`= (x^4 + x^3 - x^2) - (4x^3 + 4x^2 -4x) - (x^2 + x -1)`
`= x^2 (x^2 + x - 1) - 4x (x^2 + x - 1) - (x^2 + x - 1)`
`= (x^2 - 4x - 1)(x^2 + x- 1)`
