a)
[tex]5x^{2}(4x-1)(2x^{3}-x) = 5x^{2}(8x^{4}-4x^{2}-2x^{3}+x)=40x^{6}-10x^{5}-20x^{4}+5x^{3}[/tex]
b)
[tex](x^{3}-y)(3x^{4}y^{2}+3xy^{3}) = 3x^{7}y^{2}+3x^{4}y^{3}-3x^{4}y^{3}-3xy^{4}=3x^{7}y^{2}-3xy^{4}[/tex]
c)
[tex](a^{4}-2a+5)^{2} = (a^{4}-2a+5)(a^{4}-2a+5) =\\\\=a^{8}-2a^{5}+5a^{4}-2a^{5}+4a^{2}-10a+5a^{4}-10a+25=\\\\=a^{8}-4a^{5}+10a^{4}+4a^{2}-20a+25[/tex]
