The box of arrows, and a third dimension

Before this sitting

Can you already do this?

Two quick checks on “you will be able to…”. Right on both and this sitting becomes mixed practice, not a lecture. Wrong is useful — we keep the full sitting.

1. Ax = b is shorthand for…

   AAdding the matrix to bBMixing A's columns with the amounts in x to hit bCErasing row twoDAlways x = 0

2. Columns (1, 1) and (2, 2) cannot reach b = (1, 0) because…

   A1 is not evenBBoth columns point the same way, and (1, 0) is off that lineCMatrices cannot use zerosDb is too short