a: \(=x\left(x^2+6x+9\right)-\left(x^3+6x^2+12x+8\right)-9x\)
\(=x^3+6x^2+9x-x^3-6x^2-12x-8-9x\)
=-12x-8
b: \(=9x^2+6x+1-\left(1-6x+12x^2-8x^3\right)-6x\)
\(=9x^2+1-1+6x-12x^2+8x^3=8x^3-3x^2+6x\)
c: \(=2x^2-2x+3x-3-x^3+3x^2-3x+1+x^3+3x^2+3x+1\)
\(=8x^2+x-1\)