Subspaces Part 1: definition of a subspace

Preliminaries:
1. What is a subset?
2. How to verify a set is a subset of another set?
3. Notations and language of set theory related to subsets.
In this video, we introduce the definition of a subspace. We go through a preliminary example to figure out what do subspaces of R^2 look like, and we will continue to talk about how to verify a subset of a vector space is a subspace in later videos.

[@fanmiki8392]

谢谢，讲的很清楚！请继续上传