Design 3D Shapes: The tetrahedron!
Choose a size and make 1 Full Triangle, 1 Two edges, 1 Single edge in the same size.
Read all the steps before joining any pieces, and be sure to understand how it works. You can use pieces from other steps to help yourself check the geometry and join with the right angle.
Attach Two edges to Full Triangle at A, C, 71º angle between faces, with a small bead. You can use Single edge (step 4) to check the angle.
Attach Single edge to Full Triangle at B and Two edges at D with a small bead.