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Projection Matrix Formulas in Linear Algebra

The theory presented defines orthogonal projection matrices onto linear subspaces (lines, planes) within the domain of linear algebra, specifically concerning least squares approximation and overdetermined systems where no exact solution exists. The core principle establishes that a vector's error component is perpendicular to the column space of the coefficient matrix, leading to the derivation of symmetric idempotent ($P^2=P$) projection matrices formed by specific products involving transposes and inverses (generalized).