`a)27x^3-27x^2+18x-4`
`=27x^3-18x^2+12x-9x^2+6x-4`
`=3x(9x^2-6x+4)-(9x^2-6x+4)`
`=(3x-1)(9x^2-6x+4)`
`b)2x^3-x^2+5x+3`
`=2x^3-2x+6x+x^2-x+3`
`=2x(x^2-x+3)+x^2-x+3`
`=(2x+1)(x^2-x+3)`
`c)(x^2-3)^2+16`
`=x^4+4x^3+5x^2-4x^3-16x^2-20x+5x^2+20x+25`
`=x^2(x^2+4x+5)-4x(x^2+4x+5)+5(x^2+4x+5)`
`=(x^2-4x+5)(x^2+4x+5)`