These lectures are fantastic after you've mastered the basics of linear algebra https://www.youtube.com/watch?v=McLq1hEq3UY (convex optimization, by a very experienced and often funny lecturer)
Stephen Boyd is a very good lecturer! I watched his videos on linear dynamical systems almost a decade ago and thought he did a fantastic job. Would highly recommend.
The problem set for the stanford linear dynamic systems that he taught is also fantastic. The level of difficulty and the breadth of applications leaves you with so many tools.