JimPooley writes "The European Space Agency are conducting a feasibility study into a future mission to knock an asteroid off course. A Spanish company are planning the 'Don Quixote' mission to launch a pair of spacecraft at an asteroid. One hits the asteroid, while the other monitors it to see what happens."
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"