Trinomial Cube

Trinomial Cube is a puzzle first and algebra only later: the child rebuilds the cube layer by layer, guided by colour and by the way the pieces fit together. Faces are matched like to like, colour meeting the same colour, and a piece set in the wrong place leaves the layer uneven or blocks the last one, so the child takes it apart and begins again unaided. Years afterwards the same arrangement is recognised as the expansion of (a+b+c)3, a formula the hands already knew. It follows on from the Binomial Cube and suits the older children of the three to six group.