b[d1_,d2_]:=(-1+d1+d2)/2 +Sqrt[(-1+d1+d2)^2+d2]/2; d3[d1_1,d2_]:=b[d1,d2]+d1 (1/(d2/b[d1,d2]+1)); abb=Plot3D[d3[d1,d2],{d1,0.01,3},{d2,0.01,3}, AxesLabel->{"d1","d2","d3"},ImageSize->{400,300}];