If two right triangles each have a 30° angle, then the
triangles must be

Both are right triangles. That means they both have a 90∘ angle. They also both have a 30∘ angle.

It follows that both triangles have a 60∘ angle:

180∘−90∘−30∘=60∘.

So they have three angles in common.

The triangles are CONGRUENT as per the AAA rule of congruency.