I know that principal component analysis (PCA) and [exploratory] factor analysis (EFA) are meant to be examples of the General Linear Model, but I've never been able to find a good way of explaining this to students.
You can assume the student already understands and can read equations relating to simple regression, multiple regression, ANOVA, ANCOVA, etc. You can also assume that the student can read and understand General Linear Models
(as in the following, taken from https://en.wikipedia.org/wiki/Design_matrix) expressed in matrix form:
The student could understand statements of that sort in relation to multiple regression or ANOVA, and perhaps also in relation to more complex scenarios.
However, they don't see the link with these models and PCA or EFA.