a) \(\left(2x-1\right)\left(4x^2+2x+1\right)\)
\(=2x4x^2+2x2x+2x-4x^2-2x-1\)
\(=8x^3+4x^2+2x-4x^2-2x-1\)
\(=8x^3-1\)
b) \(\left(x+2y+z\right)\left(x+2y-z\right)\)
\(=x^2+2xy-xz+2xy+4y^2-2yz+xz+2yz-z^2\)
\(=x^2+2xy+2xy+4y^2-z^2\)
c)\(\left(x^2-3\right)\left(x^4+3x^2+9\right)\)
\(=x^6+3x^4+9x^2-3x^4-9x^2-27\)
\(=x^6-27\)