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Michael Hoppe
  • Member for 8 years, 9 months
  • Last seen this week
59 votes

Show that a matrix $A$ is singular if and only if $0$ is an eigenvalue.

33 votes

Is it faster to count to the infinite going one by one or two by two?

24 votes

Why can't $|x-2|$ be less than zero?

21 votes

How to find the orthogonal complement of a subspace?

20 votes
Accepted

Calculating limit of definite integral

19 votes

A continuous, injective function $f: \mathbb{R} \to \mathbb{R}$ is either strictly increasing or strictly decreasing.

16 votes

Continuous injective map is strictly monotonic

13 votes
Accepted

Differences between infinite-dimensional and finite-dimensional vector spaces

11 votes
Accepted

Algebraic Basis vs Hilbert basis

11 votes

Two numbers equality formula

10 votes

Finding the limit of $\frac{\sqrt{x}}{\sqrt{x}+\sin\sqrt{x}}$

10 votes

What is the relationship between blue area and red area?

9 votes

Eigenvectors are linearly independent?

9 votes

Are there mathematical concepts that exist in dimension $4$, but not in dimension $3$?

8 votes

Explain why perpendicular lines have negative reciprocal slopes

8 votes
Accepted

Crazy calculation for winding numbers

8 votes

What is the intuitive interpretation of the transpose compared to the inverse?

7 votes
Accepted

Intuition behind Variance formula

7 votes

The n-th root of a prime number is irrational

7 votes

Prove that $A\mathbf{x}=0$ has a non-zero solution $\mathbf{x}$ iff $\det(A)=0$.

7 votes
Accepted

Show that $f(x)=\sqrt 2$ has no solutions $f(x)=\sin x\cos x(2+\sin x)$ and $x\in [0,\frac{\pi}{2}]$.

7 votes

When a spade is not a spade

6 votes

How can $|x|= -x$, when $x<0$?

6 votes

Reflexivity: How can something be related to itself?

6 votes

$2\times2$ matrices are not big enough

6 votes

Show that $SO(3)$ is compact.

6 votes

Instance of Mean Value Theorem

6 votes

What exactly is a matrix?

6 votes
Accepted

When sum of two Poisson variables is not Poisson

5 votes
Accepted

How do I solve a derivative that has an absolute value $x \times |x|$

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