a)
[-(5x^4+3x^2-4x)+3x^2(2x^2-1)]*(1-2x)=
(1-2x)(-5x^4-3x^2+4x+6x^4-3x^2)=
-5x^4-3x^2+4x+6x^4-3x^2+10x^5+6x^3-8x^2-12x^5+6x^3=
-2x^5+x^4+12x^3-14x^2+4x
b)
[4x(-2x^9+7x^3)-(20x^4-8x^{10})]*[1-5(2-x^2)]=
(-8x^{10}+28x^4-20x^4+8x^{10})(1-10+5x^2)=
8x^4(5x^2-9)=40x^6-72x^4
c)
(3-4x^3)(5x^2+x)-[-5(x^5+2x^2)+x(6x^4-5x^2)]=
15x^2+3x-20x^5-4x^4-(5x^5-10x^2+6x^5-5x^3)=
-20x^5-4x^4+15x^2+3x-5x^5+10x^2-6x^5+5x^3=
-21x^5-4x^4+5x^3+25x^2+3x