The proper name for a threesided pyramid is a tetrahedron. Tetrahedrons have three showing sides formed by three triangles of equal dimensions. The base or bottom of a tetrahedron is also a triangle, whereas a real pyramid built by ancient Egyptians has a square base. Also, Egyptian pyramids have four showing triangular faces, not just three. Nevertheless, you can create threesided pyramid models, or tetrahedrons, for school and home craft projects.
Things You'll Need
 2 pieces of cardboard
 Cup of sand
 Glue
 Newspaper
 Ruler
 Scissors
 Transparent tape

Measure and draw a triangle that is 3 inches long on all three sides on a piece of cardboard. Cut it out with a pair of scissors.

Lay the cutout triangle in the center on another piece of cardboard. Trace the triangle outline on the second piece of cardboard with a pencil. Erase small segments of the pencil lines so that all three sides of the triangle outline consist of dotted lines.

Line one side of the cutout cardboard triangle along one side of the dotted triangle outline. Ensure that the sides are even, so that both triangles share a common side. Trace the outline of the two nonshared sides of the cutout cardboard triangle using a pencil.

Repeat Step 3 for the remaining two dotted sides of the center triangle. The result should look like a large triangle with four smaller triangles inside of it.

Cut out the large triangle around its outline using scissors to create the unfolded threesided pyramid. Do not cut along any dotted lines.

Fold one triangleshaped flap inwards towards the center triangle along the dotted line. Open it back up and repeat for the other two triangleshaped flaps.

Fold all three triangleshaped flaps inwards at the same time so that three tips meet in the center. Hold the tips together with your fingers. Tape each of the three corners together at the bottom using transparent tape. Tape the three tips together at the top of the threesided pyramid with transparent tape as well.

Place the threesided pyramid on a sheet of newspaper. Cover the three sides of the pyramid with a thin layer of glue, using the tip of the glue bottle as an applicator. Avoid getting glue on the bottom of the pyramid so that it does not stick to the newspaper. Pour sand over the three gluecovered sides of the pyramid. Shake the pyramid carefully to remove excess sand, using a toothpick to push it around. Allow the threesided pyramid to dry for at least one hour.

Repeat step 2 through Step 8 to make additional pyramids. Make larger pyramids by increasing the length of the cardboard triangle. Ensure that all sides of the triangle are the same length.
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