If, like me, you have been pondering linear algebra on a Christmas afternoon (and, frankly, who hasn’t?), or if you know anybody who is learning it for the first time, then I highly recommend Grant Sanderson’s YouTube channel, 3Blue1Brown where he makes all kinds of mathematical ideas easier to understand through some clever visualisations.
In particular, his Essence of linear algebra course is a wonderful presentation of the basics. Do you have vague memories of matrix multiplication and of phrases like ‘determinant’ and ‘eigenvector’ but have no idea why you learned them or what they did? Then this is the resource for you. Not only is it good revision, but it explains them in a different way from the way you might have learned them originally, which can help you get a better understanding than you had before.
Oh, and if linear algebra isn’t your idea of a fun way to spend Christmas, don’t worry. There’s Essence of Calculus as well.