1)
[tex]-3x(2x-5y)-8x=-3x\cdot2x-3x\cdot(-5y)-8x=\boxed{-6x^2+15xy-8x}\\[/tex]
2)
[tex]2ab(3a-4b)=2ab\cdot3a-2ab\cdot4b=\boxed{6a^2b-8ab^2}\\[/tex]
3)
[tex]2(5x-2y)-4(-3x+y)=2\cdot5x-2\cdot2y-4\cdot(-3x)-4\cdot y=\\\\=10x-4y+12x-4y=10x+12x-4y-4y=\boxed{22x-8y}[/tex]
4)
[tex](16x^2-20y^2):4=16x^2:4-20y^2:4=\boxed{4x^2-5y^2}[/tex]
5)
[tex]7x^2-12+5x-2xy^2-10-3x=\\\\=7x^2-2xy^2+5x-3x-12-10=\boxed{7x^2-2xy^2+2x-22}[/tex]
