diff --git a/linear_algebra/WHERE ARE THE NOTEBOOKS.txt b/linear_algebra/WHERE ARE THE NOTEBOOKS.txt
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+If you're here, this means you haven't watched the "where to get the notebooks" lecture very carefully!
+
+Please watch it again, and follow the instructions.
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diff --git a/linear_algebra/extra_reading.txt b/linear_algebra/extra_reading.txt
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+Introduction to Linear Algebra by Gilbert Strang
+https://amzn.to/2G3bvW1
+
+Still Don't Understand Gravity? This Will Help
+- this is included not because it's about calculus, but because it's yet another educator explaining why practice is important
+https://www.youtube.com/watch?v=cP2uVarXi1A
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