This depicts the SSA case for triangles, in which two sides and one of their opposite angles are given. In it's default state, the side length "a" is clearly not long enough to form a real triangle.
Adjust the slider for "a" until it is just long enough to form one triangle.
Keep on lengthening side "a" until there are two possible triangles formed by the given info (This is know as the "ambiguous" case).
Keep on lengthening it further until there is once again only one possible triangle.