Matrix

a matrix isn’t a table. it’s a thing that does something to space.

drag the two arrows and watch the whole plane stretch, shear, and fold with them

Every 2x2 matrix is completely described by where it sends two arrows: the one pointing right and the one pointing up. Wherever those land, every other point in the plane lands proportionally along with them — the whole grid stretches, shears, or flips to match. The determinant is not a separate fact you compute afterward; it is just how much the area of one square changed by watching those two arrows move, positive if the plane kept its orientation and negative if it turned inside out.

Concepts: geometry, symmetry.

An interactive you play with one thumb, on Wundr.