5*(1-y) ^3+5y*(1+y) ^2- (1-5y) ^2- (1-5y) ^2

5*(1-y) ^3+5y*(1+y) ^2- (1-5y) ^2- (1-5y) ^2=5 (1-3y+3y^2-y^3)+5y (1+2y+y^2) -1+10y-25y^2-1+10y-25y^2=5-15y+15y^2-5y^3+5y+10y^2+5y^3-1+10y-25y^2-1+10y-25y^2=-25y^2+10y+3f (y)=-25y^2+10y+3D (f)=Rf (y)=0-25y^2+10y+3=0 D=100+4*3*25=400y1=(-10+20) /-50=10/-50=-0,2y2=(-10-20) /-50=-30/-50=0,6