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MATH 01210 · Linear Algebra

MATH 01210 · Linear maps & eigenstuff

Orthogonality / projections (often)

Definition

Vectors u⊥v if u·v=0. Orthogonal sets are independent (if nonzero). Projection of b onto a: proj_a b = ((b·a)/(a·a)) a. Least squares solves AᵀAx=Aᵀb.

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Orthonormal bases make coordinates easy (Fourier-style coefficients).

QR and Gram–Schmidt build orthonormal bases from independent sets.

Orthogonal matrices: QᵀQ=I, preserve lengths/angles.

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Attempt each problem first, then open the worked solution.

  1. 1.Project (1,1) onto span{(1,0)}.