### Questions (195)

 19 Proof that $S_3$ isomorphic to $D_3$ 13 False homework proof?: The image of an element has the same order. 10 Rigorous proof that surjectivity implies injectivity for finite sets 9 What application is there for a non-Hausdorff topological space? 8 Find all matrices which satisfy $M^2-3M+3I = 0$

### Reputation (3,724)

 +10 Locally Lipschitz $\Rightarrow$ uniqueness; globally Lipschitz $\Rightarrow$ existence and uniqueness? -2 Proof from the definition that the outer measure of any open set is the sum over its interval lengths. +10 Are there integer solutions for $x$ in the equation $n^2+9n-2=(n+11)x$ for $0\le n\le 11$? +10 Valid rearrangements of infinite series — where is the bijection when you split up a series?

 5 matrix multiplication: $A^2 = A$? 5 What does non-zero integer mean? 4 Suppose that 0 < a < b. Prove that $a < \sqrt{ab} < b$ and $\sqrt{ab} \leq \frac{1}{2}(a+b)$ 3 Does there exist a system such that the additive identity is non-zero? 2 Is $R$ reflexive, symmetric, and transitive?

### Tags (190)

 6 elementary-set-theory × 7 4 real-analysis × 23 5 linear-algebra × 14 4 proof-writing × 3 5 matrices × 8 3 logic × 16 5 proof-verification × 3 3 discrete-mathematics × 5 5 terminology × 2 3 arithmetic × 2

### Bookmarks (2)

 4 Let $G$ a group and $g,h∈G$. Prove that $|gh|=|hg|$. [duplicate] 1 Integrate with square root in square