In the tetrahedron ABCD , AB = BC =10 , $\displaystyle AC=8\sqrt{2}$ , AD=CD=8 cm and BD = 6 cm . Show that the line from C perpendicular to AB and the line from D perpendicular to AB meet at a point AB .

I can see from the sketch and deduce that they meet at the same point . But how can i show mathematically . THanks !!