>>24625459
It's interesting, sometimes the proofs are a bit surprising, like an early one in book 1 that amounts to demonstrating that two triangles with equal sides and an equal angle will be equal as triangles by just moving one of them on top of the other and going, "...see?" Books 5 and 7 have a lot of overlap (they're both on ratios, but one treats magnitudes and the other treats numbers), and a lot of use in music theory and astronomy. The final book with all the Platonic solids is exhausting but really cool.