a)
w(x)=5x^5-20x^3=5x^3(x^2-4)=5x^3(x-2)(x+2)
b)
w(x)=x^5-125x^2=x^2(x^3-125)=x^2(x^3-5^3)=x^2(x-5)(x^2+5x+25)
c)
w(x)=-5x^5+30x^4-45x^3=-5x^3(x^2-6x+9)=-5x^3(x-3)^2
d)
w(x)=2x^5+8x^4-10x^3=2x^3(x^2+4x-5)=2x^3(x^2-x+5x-5)=
=2x^3[x(x-1)+5(x-1)]=2x^3(x-1)(x+5)