If you only know 2 sides of 2 triangles and they are both proportional, but you have no other information, can you know if they're similar or not (and if so, reference image:

The answer to the question you asked is, "no, two sides is insufficient information to determine similarity."

The answer to the given figure is that the triangles are similar because you have two proportional sides and the angle between them.

Step-by-step explanation:

The vertical angles where the lines cross are congruent, so the triangles are similar by the SAS theorem.