loes=NSolve[2 c^3/(c^2-1)==15,c]; a=c/.loes[[2]]; r1=2 a^3/(1+a^2)^2; q1=2 a^3/(a^2-1); g1[u_]=r1(1-u/q1); b=c/.loes[[1]]; r2=2 b^3/(1+b^2)^2; q2=2 b^3/(b^2-1); g2[u_]=r2(1-u/q2); h[u_]=u/(1+u^2); q=Min[q1,q2]; abb=Plot[{g1[u],g2[u],h[u]},{u,0,q},ImageSize->{400,300}];