I'd say that, if the angles S and U are equal, as the SV and UV segments move towards each other, they meet at vertex V, the angles they make, angle SVT and UVT, have to be equal, because the side TV is shared by both, and has the same direction.
now, side TV is on both triangles, and is shared by both, so is the same length, so TV on one triangle is equal to TV on the other
check the picture below
so, you have one Angle, another Angle, and then a Side
A A S