Linear Algebra · Advanced · 11 min

Orthogonality

Orthogonal decomposition splits a vector into independent perpendicular contributions.

WHAT HAPPENS IF…For u=(3,0,0), what is the parallel part?
Interactive exploration
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Connect the picture to the ideau=proj⁡nu+(u−proj⁡nu)u=\operatorname{proj}_n u+\left(u-\operatorname{proj}_n u\right)

With n=(1,2,2), n·n=9. The parallel part is [(u·n)/9]n and the remainder has dot product zero with n. The components are orthogonal, so their squared lengths add to ||u||². The displayed plane represents all vectors perpendicular to n.

A detail that matters

Zero is orthogonal to every vector but has no direction.

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