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124
Sum of two closed sets in $\mathbb R$ is closed?
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117
How can I evaluate $\sum_{n=0}^\infty(n+1)x^n$?
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95
An open ball is an open set
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74
Your favourite application of the Baire Category Theorem
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72
Why is an average of an average usually incorrect?
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66
How to determine if a function is one-to-one?
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63
How do I calculate Euclidean and Manhattan distance by hand?
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62
The space of bounded continuous functions are not separable
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60
Determining variance from sum of two random correlated variables
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60
Finding the basis of a null space
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56
Are these two Banach spaces isometrically isomorphic?
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48
Calculate point, given x, y, angle, and distance
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44
Why is this series of square root of twos equal $\pi$?
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43
Prove that the equation $x^{10000} + x^{100} - 1 = 0$ has a solution with $0 < x < 1$
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40
Is sin(x) necessarily irrational where x is rational?
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40
Positive series problem: $\sum\limits_{n\geq1}a_n=+\infty$ implies $\sum_{n\geq1}\frac{a_n}{1+a_n}=+\infty$
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39
Why $\lim \limits_ {n\to \infty}\left (\frac{n+3}{n+4}\right)^n \neq 1$?
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37
Linear functional on a Banach space is discontinuous then its nullspace is dense.
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35
Choose a random number between $0$ and $1$ and record its value. Keep doing it until the sum of the numbers exceeds $1$. How many tries do we need?
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35
Why doesn't $d(x_n,x_{n+1})\rightarrow 0$ as $n\rightarrow\infty$ imply ${x_n}$ is Cauchy?
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35
$f$ uniformly continuous and $\int_a^\infty f(x)\,dx$ converges imply $\lim_{x \to \infty} f(x) = 0$
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34
why is ${n+1\choose k} = {n\choose k} + {n\choose k-1}$?
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34
What is an example that a function is differentiable but derivative is not Riemann integrable
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31
Why $x<\tan{x}$ while $0<x<\frac{\pi}{2}$?
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30
How to remember the trigonometric identities
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30
If we define $\sin x$ as series, how can we obtain the geometric meaning of $\sin x$?
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28
Is $\int_a^b f(x) dx = \int_{f(a)}^{f(b)} f^{-1}(x) dx$?
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27
Describe the interior of Cantor set
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27
Statistics: Could someone show why this exponential pdf integrates into this particular cdf
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26
Proving $(1 + 1/n)^{n+1} \gt e$
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