For the book, you may refer: https://amzn.to/3aT4ino
This lecture explains the quadratic form and their definiteness such as positive definite, positive semi-definite, negative definite, negative semi-definite, and indefiniteness.
Other videos:
Quadratic form: https://youtu.be/6jjTLDX_JOk
Hessian Matrix: https://youtu.be/mJB-XLV0QJc
Convex & Concave function: https://youtu.be/nZ7vjo2dQ1o
Maxima & Minima of the function: https://youtu.be/gJHgIcMeS2M
