"Eigenvalues and eigenvectors" sounds like the scariest part of linear algebra, and a lot of courses introduce it with dense proofs that make it feel that way. The actual idea is simpler than the name suggests: when a matrix transforms a vector, most vectors get both stretched and rotated — but a special few only get stretched, never rotated. Those special directions are eigenvectors, and how much they get stretched is the eigenvalue.
1-A 2-A 3-A 4-A | 5 lambda 6 direction 7 = 3 and 7 (diagonal) 8 = They are the directions of maximum variance in the data 9 = That direction is unchanged in length | 10 = Flips the direction while scaling