Linked from
The 36 pages that link to Cauchy–Schwarz inequality, each with the reason it gives.
Inner product spaceRelated: It ensures the inner-product norm obeys the triangle inequality.
Gram matrixRelated: It bounds each Gram entry by the corresponding diagonal entries.
AM–GM inequalityRelated: Repeated applications yield common proofs of AM–GM for powers of two terms.
Euclidean vectorRelated: It constrains possible angles and underpins the Euclidean distance formula.