A resource for replenishing knowledge?

Question

Mathematics

Is there any site where information is concentrated on the basic rules of mathematics, physics, Russian and other subjects

Answer 1

Wikipedia, studopediya, intuit.

Answer 2

Knowledge cannot be obtained that way.

Answer 3

Recently I watched geometry avidly here:
https://www.youtube.com/user/KhanAcademyRussian/pl...
Probably not everything there, but as a memory freshener - it went to me.