### Answers (1,949)

 85 Why are two planes parallel to the same line not necessarily parallel? 72 What is the most unusual proof you know that $\sqrt{2}$ is irrational? 65 Is there an “inverted” dot product? 35 Creating a question that use the $\epsilon$-$\delta$ definition to prove that $f$ is a continuous function 31 Are all bilinear forms identically zero?

### Reputation (66,229)

 +10 Example of a space that is locally homeomorhpic to $\mathbb{R}^n$ but not Hausdorff +10 Derivative of Gauss map is the second fundamental form +10 Prove Or Disprove: tr(AB)=tr(A)*tr(B) +10 Finding Lipschitz for trigonometric functions

### Questions (227)

 31 Orientability of $m\times n$ matrices with rank $r$ 19 Proving that a doubly-periodic entire function $f$ is constant. 16 Gathering books on Lorentzian Geometry 15 Does the graph of a measurable function always have zero measure? 14 Distance to a closed set is continuous.

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 820 linear-algebra × 368 289 general-topology × 115 661 real-analysis × 279 277 riemannian-geometry × 150 655 differential-geometry × 421 242 matrices × 95 581 calculus × 271 224 derivatives × 119 292 multivariable-calculus × 206 197 integration × 88

### Bookmarks (434)

 802 How to study math to really understand it and have a healthy lifestyle with free time? [closed] 761 Different methods to compute $\sum\limits_{k=1}^\infty \frac{1}{k^2}$ (Basel problem) 478 “The Egg:” Bizarre behavior of the roots of a family of polynomials. 451 Best Sets of Lecture Notes and Articles 323 A challenge by R. P. Feynman: give counter-intuitive theorems that can be translated into everyday language

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