Here we will collect images, videos, and tools which I think are potentially useful.
Introduction to double integrals — Have a look at the images and movies here https://instruct.math.lsa.umich.edu/lecturedemos/ma215/docs/15_2/examples.html.
Double integration theory — I wrote you all a little supplemental note here: double_integral_theory
Spherical coordinates online tool visualizer:
https://mathinsight.org/spherical_coordinates
Practice midterm: Math 23b Practice Midterm
Practice Midterm solutions:
23b_practice_midterm_solutions_2-3