http://www.tech.plym.ac.uk/sme/THER204B-web/Heatran1.PDF

xA = 1;
xB = 5;
yA = 3;
yB = 3;
el1 = (Sqrt[(((ox - xA))^2) + (yA^2)]);
el2 = (Sqrt[(((ox - xB))^2) + (yB^2)]);
Plot[el1 + el2, {ox, xA, xB}, 
        PlotStyle -> {Hue[0.6], Thickness[0.008]}, 
        AxesLabel -> {"ox", "t"}];

v1 = 1;
v2 = Random[];
Plot[(el1/v1) + (el2/v2), {ox, xA, xB}, 
        PlotStyle -> {Hue[0.6], Thickness[0.008]}, 
        AxesLabel -> {"ox", "t"}, 
        PlotRange -> All];

oxMin = 
      ox /. FindMinimum[
            (el1/v1) + (el2/v2), {ox, xA, xB}][[2]]

sinα1 = 
        Sin[ArcTan[((oxMin - xA)/yA)]];
sinα2 = 
        Sin[ArcTan[((xB - oxMin)/yB)]];
\(Print[\*""\!\(sinα1\/sinα2\)= "", 
      sinα1\/sinα2, \*""   \!\(v1\/v2\)= "", 
      v1\/v2]\)