Law of Sines
Here's a teaching tool designed to help a math teacher illustrate how in the law of sines, with a fixed angle a and length A, there can be two different angles b & c and sides B & C.
The first image shows and example of an instance where there is only one answer because A intersects B at a right angle (to make the math easier, the length of the hypotenuse, C is 10 inches so this is a 3-4-5 triangle. Therefore the white tape mark is at 6)
The second and third images show the same angle a but using the blue tape mark at 8 there can be two different triangles with the same angle a and length A.