Which mathematical concept revolutionized online shopping by enabling the 'recommendation engines' now used by major retailers like Amazon?

Mathematics has transformed how retail products are developed, marketed, and sold. From inventory optimization algorithms to predictive analytics for consumer behavior, mathematical tools have become essential in the retail industry. This poll tests your knowledge about how mathematical concepts have influenced major product developments and consumer experiences in the marketplace. Can you calculate the correct answer?

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Collaborative filtering algorithms
Differential calculus
Euclidean geometry
Bayesian probability (without machine learning integration)