((а+1)*(а-1))/а+а/(а-1)=((а+1)*(а-1)+а*а)/(а*(а-1))=(2а^2-1)/(a^2-1). 0,5*0,5=0,25. (2*0,25-1)/(0,25-1`)=(-0,5)/(-0,75)=2/3.
6x^3y^2/15xy^3=2x^2/5y, (y^2-2y+1)/(1-y^2)=(y-1)^2/((1-y)*(1+y))=-(y-1)^2/((y-1)*(1+y))=-(y-1)/(1+y)=(1-y)/(1+y), 2*(b+9)/(b+9)^2=2/(b+9)