Lecture 13: Lagrange multipliers
Mathematics of Machine Learning
Topics in Mathematics of Data Science
Lecture 10: Second derivative test; boundaries and infinity
Active Calculus Multivariable
Algebra and Trigonometry: OpenStax
Prealgebra: OpenStax
Light, charges and brains
Lecture 8: Level curves; partial derivatives; tangent plane approximation
College Algebra: OpenStax