r1[c_]:=-c^2+5c/2+1/8 + (c-1/8) Sqrt[1-8c];
r2[c_]:=-c^2+5c/2+1/8 - (c-1/8) Sqrt[1-8c];
abb=Plot[{r1[c],r2[c]},{c,0,1/8},AxesLabel->{"c","r_+,r_-"},
ImageSize->{400,300}]