19) x^2-2x-3=0, (x^2-2x-3)/(x^2+2x+1)=(x-3)(x+1)/(x+1)^2=(x-3)/(x+1).
D=1+3=4=2^2,
x1=1+2=3,
x2=1-2=-1,
x^2-2x-3=(x-3)(x+1),
22) a) 5b/*6a=(5b*2ab)/(6a*2ab)=10ab^2/12a^2b,
c) 2a/3b=(2a*4a^2)/(3b*4a^2)=8a^3/12a^2b.
23) 7x/6y=(7x*2x^2y^2)/(6y*2x^2y^2)=14x^3y^2/12x^2y^3