Ask HN: Math books that made you significantly better at math?

Yes, we can construct such a line segment; but line segments are not numbers.

We don't actually need "legs of length one" (which pre-supposes some system of units); all we need is the ratio of the lengths of the sides. However, finding lengths requires the ability to take square roots, which would either make this a circular definition (e.g. that √2 = √2 / 1), or requires the limit of an infinite process (like Newton's method, or equivalent).

Instead, it's much easier to count the areas of the squares on each leg (1 and 1), and add them together to get the area of the square on the hypotenuse (1 + 1 = 2). No need for lengths, so no need for square roots, so no need for √2.

Wildberger abbreviates 'area of the square on a segment/vector' as the 'quadrance' of that segment/vector (defined as the dot-product with itself). Likewise we can avoid angles by taking ratios of quadrances (e.g. 'spread' is defined via a right-triangle as the quadrance of the opposite side / quadrance of the hypotenuse); together this gives rise to a whole theory of Rational Trigonometry, which gives efficiently computable, exact answers; works in arbitrary fields (except for characteristic two), and with arbitrary dot-products/bilinear-forms (e.g. euclidean, relativistic, spherical, etc.). Here's Wildberger's textbook on the subject http://www.ms.lt/derlius/WildbergerDivineProportions.pdf

Paperback layout feels like a workbook, not overwhelming-- beginner friendly

I finally learned the point behind math thanks to dabbling in programming. All the math classes and teachers and textbooks in the world will never teach me what the importance of 1+1 is.

I was so accustomed to hearing that mathematics is nothing if not rigorous, but the more I reflect, mathematics is much more dependent on social convention and agreement amongst a community. While an outsider might think that proofs rigorously establish theorems, the purpose of a proof might be better seen as having enough detail to convince a substantial portion of the prominent mathematicians in a field that the proof is correct. In fact, there are theorems (e.g. the ABC conjecture) where a “proof” has been proposed, but not enough mathematicians have expertise with the techniques used to prove it in order to agree whether the proof is sufficient or not (though I’ve heard that the general opinion is that the proof does not suffice). William Thurston wrote one of my favorite essays related to this topic: https://www.math.toronto.edu/mccann/199/thurston.pdf

Reflecting on my own experience in mathematics, a better way to think of proofs is as being composed of “thought patterns” which many mathematicians agree are likely to be correct - when I scan a proof, I don’t look through every detail to verify that it is correct, but rather run it through a series of high level tests to see if it fails in any way, then if it passes all of those I look more closely at the argument and analyze the structure and mathematical power of each statement (e.g. one is unlikely to establish a hard analytic result through purely algebraic means, so where is the magic going on?) and so on until I’ve convinced myself that the argument is probably true. Other times, the result may be “visually apparent” (e.g. in geometry) at which point it might be sufficient for me to just to connect certain canonical arguments with the pictures as I read through the proof. For an excellent overview of this process, read Terry Tao’s blog on identifying errors in proofs : https://terrytao.wordpress.com/advice-on-writing-papers/on-l....

I don’t feel as confident commenting on the programming/computational perspective, as I’ve probably developed a very idiosyncratic way of thinking from approaching the topic so late in my education, but my feeling is that they are much different, and that the types of things a mathematician wants to convey to another mathematician rely much more on “trust” rather than the kind of rigor that might be needed by a computer.

I think this would be an interesting topic to explore in longer form.

Not as colorful and attractive but the adage "do not judge a book by its cover" applies so well to this masterpiece. With brief and precise explanations and high quality exercises with solutions, I went from struggling to getting A+