`c,`

`-8x^2+5x+3`

`= -(8x^2-5x-3)`

`= -(8x^2-8x+3x-3)`

`= -[8x(x-1)+3(x-1)]`

`= -(x-1)(8x+3)`

`d,`

`3x^2+3x-6`

`= 3(x^2+x-2)`

`= 3(x^2-x+2x-2)`

`= 3.[x(x-1)+2(x-1)]`

`= 3(x-1)(x+2)`

`e,`

`x^4-7x^2+6`

`= x^4-x^3+x^3-x^2-6x^2+6x-6x+6`

`= x^3(x-1)+x^2(x-1)-6x(x-1)-6(x-1)`

`= (x-1)(x^3+x^2-6x-6)`

`= (x-1).[x^2(x+1)-6(x+1)]`

`= (x-1)(x+1)(x^2-6)`

`d,`

`x^4+x^2+1`

`= x^4-x+x^2+x+1`

`= x(x^3-1)+x^2+x+1`

`= x(x-1)(x^2+x+1)+(x^2+x+1)`

`= (x^2+x+1).[x(x-1)+1]`

`= (x^2+x+1)(x^2-x+1)`

`#TD`