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+3

f(y)=-25y^2+10y+3

D(f)=R

f(y)=0

-25y^2+10y+3=0 

D=100+4*3*25=400

y1=(-10+20)/-50=10/-50=-0,2

y2=(-10-20)/-50=-30/-50=0,6