19)y*=9x^-4-60x^-5+6x^-4-x^-2
20)y*=(x^-3/4-3x^-1/3+2x^2+x^-1+8)*=-3/4x^-7/4+x^-4/3+4x-x^-2
21) f(x)=(2x+1)(x^2+3x-1)=2x^3+8x^2+x-1
f(x)*=6x^2+16x+1 ; f(x)=(x^3+x^2+x+1)*(x-1)=x^4-x; f(x)*=4x^3-x
22) f*(x)= ((x^-2)/(2-x^2))*=(-2x^-3*(-2x)-x^-2*(-2x))/(2-x^2)2=(4x^-2+2x^-1)/(2-x^2)^2
y=(x^2-x+1)/(x^3+1)=(x^2-x+1)/(x+1)(x^2-x+1)=1/(x+1), y*=-1/(x+1)^2