### Questions (13)

 54 Geometric interpretation for complex eigenvectors of a 2×2 rotation matrix 23 Best books in the genre “______ for Mathematicians” 15 Combinatorial proof that binomial coefficients are given by alternating sums of squares? 12 Topic for a high school-level math elective? 9 Does this “extension property” for polynomial rings satisfy a universal property?

### Reputation (1,407)

 +20 Geometric interpretation for complex eigenvectors of a 2×2 rotation matrix +5 Combinatorial proof that binomial coefficients are given by alternating sums of squares? +5 Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? +5 Does this “extension property” for polynomial rings satisfy a universal property?

### Answers (9)

 24 Why do we need to prove $e^{u+v} = e^ue^v$? 11 solving integral $\int{{3^x}{e^x}dx}$ 6 Why do we define quotient groups for normal subgroups only? 5 Is there a “canonical” representation of integers using numbers other than primes? 4 Is there a way to pick a $k$ such that $p_0p_1 + ik$ is always a product of two primes?

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 24 education × 5 6 normal-subgroups 24 exponentiation 6 quotient-group 11 integration 5 prime-numbers 11 calculus 4 abstract-algebra × 2 6 group-theory 4 elementary-number-theory

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