a)
[tex](x-5)(x+1)(2-x)=(x^2+x-5x-5)(2-x)=\\\\=(x^2-4x-5)(2-x)=2x^2-x^3-8x+4x^2-10+5x=\\\\=\boxed{-x^3+6x^2-3x-10}[/tex]
b)
[tex](4x^2-1)(x+3)(1-x^2)=(4x^3+12x^2-x-3)(1-x^2)=\\\\=4x^3-4x^5+12x^2-12x^4-x+x^3-3+3x^2=\\\\=\boxed{-4x^5-12x^4+5x^3+15x^2-x-3}[/tex]
