Sorted from top to bottom and from left to right, the numbers 1 and 5 and 6 in the first picture are definitely not opposite.

Then, consider a square with the number 2. As can be seen from the figure below, the numbers 2 and 4 are opposite, and 5 and 6 are opposite, so the number 1 can only be opposite to the number 3.

Extended data:

Plane expansion diagram with 1 1 cubes. The following is the way to understand and master these cubic 1 1 planar expansion diagrams:

We know that a cube has six faces, and each face is the same square. We discharge six identical small squares from the plane figure of the possible expansion diagram of the cube. There are 35 plane figures.

Then start the operation, fold in turn, exclude the plane graphics that cannot be folded into cubes, and keep the plane graphics that can be folded into cubes. The preserved figure is the plane expansion of the cube. By folding, the color 1 1 plane graphics on the right can be folded into cubes, so they are the plane development diagrams of cubes.

There are 1 1 kinds of planar expansion diagrams of cubes, and it is not easy to remember them all. In order to better grasp the memory, we can divide these 1 1 expansion diagrams into four categories. As long as you grasp the characteristics of each category, it is easy to remember.

The first category: four sides in the middle, one on each side, ***6 species.

The second category: three sides in the middle, one or two on each side, three kinds of * * *. ?

The third category: two connected squares in the middle, two on each side, only 1 species. Category IV: three species in two rows, only 1 species.

Properties of regular tetrahedron;

1, every face of a regular tetrahedron is a regular triangle, and vice versa.

2. Regular tetrahedrons are three groups of equilateral tetrahedrons perpendicular to the edges.

3. Regular tetrahedron is two groups of equilateral tetrahedrons perpendicular to edges.

4. The lines connecting the midpoints of the regular tetrahedron are perpendicular and equal to each other, equal to twice the side length, and vice versa.

5. The midpoint of each side of a regular tetrahedron is the six vertices of a regular octahedron.