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๐Ÿ“ Baby-Step Giant-Step Algorithm Compute discrete log in $O(\\sqrt{n})$ time and space, where $n = |G|$. Proof: Set $m = \\lceil\\sqrt{n}\\rceil$. Baby steps: compute $g^0, g^1, \\ldots, g^{m-1}$ and store in table. Giant steps: compute $hg^{-m}, hg^{-2m}, \\ldots$ until match found. If $g^j = hg^{-im}$, then $x = im + j$. At most $m$ steps of each type, so $O(\\sqrt{n})$ total. From: Algebraic Number Theory Learn more: Explore all courses:
๐Ÿ“ Theorem 3.2.1 (Russell There is no "set of all sets." More precisely, if we assume a universal set $\\Omega$ exists (containing all objects), we get a contradiction. Proof: Suppose for sake of contradiction that a universal set $\\Omega$ exists. Define $S := \\{x \\in \\Omega : x \\notin x\\}$. Since $S \\in \\Omega$ (by universality), we can ask: is $S \\in S$? - If $S \\in S$, then by definition of $S$, we have $S \\notin S$. Contradiction! - If $S \\notin S$, t... From: tao-analysis-1 Learn more: Explore all courses:
๐Ÿ“ Newton To find roots of $f(x) = 0$, iterate: $x_{n+1} = x_n - \\frac{f(x_n)}{f\ Proof: The tangent line to $y = f(x)$ at $x_n$ has equation: $y - f(x_n) = f'(x_n)(x - x_n)$ Setting $y = 0$ (finding x-intercept): $-f(x_n) = f'(x_n)(x - x_n)$ $x = x_n - \\frac{f(x_n)}{f'(x_n)}$ This x-intercept becomes our next approximation $x_{n+1}$. From: Men of Mathematics Learn more: Explore all courses:
๐Ÿ’ก Fiduciary Duty vs. Job Security While executives are legally bound to fiduciary duties, job security often proves a more powerful incentive in practice. This explains why institutional actors may not optimize for shareholder value when facing reputational risks. From: bfi Learn more: Explore all courses:
๐Ÿ“– Supply Chain Attack A cyberattack that targets the less-secure elements in the supply network, such as third-party vendors, open-source libraries, build systems, or distribution channels. The attack is then propagated to all users of the compromised component. From: branta Learn more: Explore all courses:
๐Ÿ’ก The Corruption of Science When science becomes dependent on government, it loses independence and becomes a tool of political manipulation rather than truth-seeking. From: Atlas Shrugged Learn more: Explore all courses:
๐Ÿ“– Pointwise Convergence $(f_n)$ converges pointwise to $f$ if $\\forall x, \\forall \\varepsilon > 0, \\exists N: n > N \\Rightarrow |f_n(x) - f(x)| < \\varepsilon$. From: Real Analysis Learn more: Explore all courses:
๐Ÿ“ Rank-Nullity Theorem (Dimension Theorem) For an $m \\times n$ matrix $A$ with rank $r$: $\\dim(C(A)) + \\dim(N(A)) = n$, or equivalently, $r + (n - r) = n$. Proof: The rank $r$ equals the number of pivot columns. The nullity (dimension of $N(A)$) equals the number of free variables, which is $n - r$. Thus $r + (n - r) = n$. From: Linear Algebra Learn more: Explore all courses:
๐Ÿ“ Euclid If $p = 2^n - 1$ is prime (Mersenne prime), then $2^{n-1} \\cdot p$ is perfect. Proof: Let $N = 2^{n-1}(2^n - 1)$ where $p = 2^n - 1$ is prime. Sum of divisors of $N$ is $(1 + 2 + \\cdots + 2^{n-1})(1 + p) = (2^n - 1)(2^n)$. $= 2^n(2^n - 1) = 2 \\cdot 2^{n-1}(2^n - 1) = 2N$. Sum of proper divisors = $2N - N = N$, so $N$ is perfect. From: numbers-geometry Learn more: Explore all courses:
๐Ÿ“ Integration of sinยฒ(x) Using the identity $\\sin^2(x) = \\frac{1 - \\cos(2x)}{2}$, we have $\\int \\sin^2(x) \\, dx = \\frac{x}{2} - \\frac{\\sin(2x)}{4} + C$. From: Beginner Calculus Learn more: Explore all courses:
๐Ÿ’ก Equilateral Triangle Construction Given segment $AB$, an equilateral triangle can be constructed with $AB$ as one side. Proof: Draw circle centered at $A$ with radius $AB$. Draw circle centered at $B$ with radius $BA$. Let $C$ be an intersection point of these circles. Then $AC = AB$ (radius of first circle) and $BC = BA$ (radius of second). Therefore $AB = BC = CA$, so triangle $ABC$ is equilateral. From: numbers-geometry Learn more: Explore all courses:
๐Ÿ“ Rank-Nullity Theorem For a linear transformation $T: V \\to W$ where $V$ is finite-dimensional: $\\dim(V) = \\text{rank}(T) + \\text{nullity}(T)$. Proof: Let $\\dim(V) = n$ and $\\dim(\\ker(T)) = k$. Let $\\{v_1, \\ldots, v_k\\}$ be a basis for $\\ker(T)$. Extend this to a basis $\\{v_1, \\ldots, v_k, u_1, \\ldots, u_{n-k}\\}$ of $V$. **Claim:** $\\{T(u_1), \\ldots, T(u_{n-k})\\}$ is a basis for $\\text{im}(T)$. **Spanning:** Any $w \\in \\text... From: Advanced Linear Algebra Learn more: Explore all courses:
๐Ÿ“ Theorem 11.9.1 (First Fundamental Theorem of Calculus) Let $f : [a, b] \\to \\mathbb{R}$ be Riemann integrable, and define $F(x) := \\int_a^x f$. Then $F$ is continuous on $[a, b]$. Moreover, if $f$ is continuous at $x_0 \\in (a, b)$, then $F$ is differentiable at $x_0$ with $F\ Proof: **Continuity:** For $x < y$, $|F(y) - F(x)| = |\\int_x^y f| \\leq M(y - x)$ where $M$ bounds $|f|$. As $y \\to x$, $F(y) \\to F(x)$. **Differentiability:** Fix $x_0$ where $f$ is continuous. For $h > 0$: $\\frac{F(x_0 + h) - F(x_0)}{h} = \\frac{1}{h} \\int_{x_0}^{x_0 + h} f$ Since $f$ is conti... From: tao-analysis-1 Learn more: Explore all courses:
๐Ÿ“ Projection Theorem If $S$ is a closed subspace of an inner product space $V$ and $v \\in V$, there exists a unique $s \\in S$ such that $\\|v - s\\| = \\inf\\{\\|v - w\\| : w \\in S\\}$. Moreover, $v - s \\perp S$. Proof: The infimum is achieved by completeness of $S$. Uniqueness follows from the parallelogram law. The orthogonality condition characterizes the projection. From: adv_linalg Learn more: Explore all courses:
๐Ÿ“– Axiom 3.1 (Sets are Objects) If $A$ is a set, then $A$ is also an object. In particular, given two sets $A$ and $B$, it is meaningful to ask whether $A$ is also an element of $B$. From: tao-analysis-1 Learn more: Explore all courses:
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