For the book, you may refer: https://amzn.to/3aT4ino
This lecture will explain how to find the maxima or Minima of a function using the Lagrange multiplier method with one equality constraint.
Other lectures:
Lagrange Multiplier method with Two constraints: https://youtu.be/1QWMGllthi4
Lagrange Multiplier method with One constraint: https://youtu.be/5m32gu6qGIU
Maxima & Minima of the function: https://youtu.be/gJHgIcMeS2M
Convex & Concave function: https://youtu.be/nZ7vjo2dQ1o
Hessian Matrix: https://youtu.be/mJB-XLV0QJc
Quadratic form: https://youtu.be/6jjTLDX_JOk