Linear Algebra and Its Applications · Problem 3.2.9

Orthogonality — Gilbert Strang

Mathematics · cosines-projections-onto-lines

Problem

Square the matrix P=aaT/aTaP = aa^T/a^Ta, which projects onto a line, and show that P2=PP^2 = P. (Note the number aTaa^Ta in the middle of the matrix aaTaaTaa^Taa^T!)

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