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This sounds as a very basic question, I guess I just don't know proper terms to find the answer at once..

I'd like to create a complex polyhedron, so I'd like to create a tetrahedron first. Starting from a cube, I can get a figure like the one below (by deleting some faces and edges), but how do I connect those vertices with 3 missing edges?

Although the main question is the one in the title, other advices about creating a tetrahedron are welcome, too.

enter image description here

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    $\begingroup$ Try selecting the two vertices you want to connect and press F of the keyboard. The same tool can be used to connect two edges with faces. $\endgroup$ – CyberBurst Oct 21 '16 at 14:17
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    $\begingroup$ related: blender.stackexchange.com/a/10729/19287 $\endgroup$ – Dan Oct 21 '16 at 14:47
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The answer is simple. Just press F between two vertices.

And your tetrahedron problem can be solved as follows:

  • Start with a Plane.

  • Delete one vertex and join all vertices with F to make a triangle.

  • Subdivide the triangle.

  • Go to the outer vertices and scale them on the xy axis to 0.

  • In the last step you only have to move the selected vertices on the Z axis by one.

Enter image description here

That's it.

(Of course, don't forget to swap normals.)

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    $\begingroup$ it is not completly a tetrahedron =( the edges are not all equally long.... bad answer $\endgroup$ – Ruben Nunez Oct 21 '16 at 14:45
  • $\begingroup$ Right, so it's the F button. But what's the name of the operation? $\endgroup$ – YakovL Oct 21 '16 at 16:08
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    $\begingroup$ the name is [Make Edge/Face] press space and write the function name.... =) $\endgroup$ – Ruben Nunez Oct 21 '16 at 18:41
  • $\begingroup$ F is to form a face, if you want to join 2 vertices to make an edge, better to press J $\endgroup$ – Eric Brochu Jun 4 '19 at 21:37
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There is already a tetrahedron hiding inside the Blender default cube:

Enter image description here

Note: With two vertices selected, hitting the F key will create an edge between them. With more than two vertices selected hitting the F key will create a face. F = Fill (fills in the space between selected).

Revealing the tetrahedron:

  • Select the three vertices that make up the blue triangle and hit the F key.
  • Repeat for the yellow, pink and the fourth triangle.
  • Delete the four vertices of the cube that are not being used.
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  • $\begingroup$ Nice, I should have thought about this one :) An unfortunate thing is that we still have to use approximate values of a rotation angle to put this one on its face and use 2 rotations for that.. $\endgroup$ – YakovL Oct 21 '16 at 22:24
  • $\begingroup$ @yakovl You can come pretty close by locking one axis instead of two. In object mode, you can do r45 (or r-45) and then cycle through X, Y, Z until you get the shape normal to the ground. I haven't figured out how to express that final 90 degree rotation to make it parallel to the ground, because it needs to rotate along multiple axis there. If you could somehow rotate 45 degrees along one axis and -45 along another simultaneously, you could do it. $\endgroup$ – jpaugh Dec 16 '20 at 3:48
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For the sake of completion you can do a tetrahedron directly by enabling the Add Mesh Extra Objects Addon:

enter image description here

On the 3D viewport you can then add>Math Function>Regular Solids and choose a Tetrahedron from the Toolbar (or on the F6 Menu)

enter image description here

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