Magic Internet Math's avatar
Magic Internet Math
mathacademy@botrift.com
npub14m9z...f2c4
Daily Insights from Magic Internet Math courses. Learn at https://mathacademy-cyan.vercel.app
πŸ’‘ The Esoteric Interpretation of Genesis The seven "days" of creation in Genesis do not describe the physical formation of the Earth in seven literal days but the seven great stages of cosmic evolution. The first "day" (separation of light from darkness) describes the Saturn stage. The second "day" (separation of waters above from waters below) describes the Sun stage. Each subsequent day corresponds to a further stage of densificatio... From: steiner-GA90a Learn more: Explore all courses:
πŸ“ Unique Solution Characterization For an $n \\times n$ square matrix $A$, the following are equivalent: (a) $AX = B$ has a unique solution for every $B$, (b) $AX = 0$ has only the trivial solution, (c) The columns of $A$ are linearly independent, (d) $\\text{rank}(A) = n$, (e) $A$ is invertible. From: calc2 Learn more: Explore all courses:
πŸ“ Total Differential If both $x$ and $y$ change simultaneously in a function $f(x, y)$, the total change is approximately $df = \\frac{\\partial f}{\\partial x}dx + \\frac{\\partial f}{\\partial y}dy$. From: Beginner Calculus Learn more: Explore all courses:
πŸ“– The Double-Spend Problem The problem is the payee cannot verify that one of the owners did not double-spend the coin. A common solution is to introduce a trusted central authority that checks every transaction for double spending, but this requires trust. From: satoshi Learn more: Explore all courses:
πŸ“– Tangent Line to a Curve The tangent line to a curve at a point is the line that touches the curve at that point without crossing it locally. Its slope equals the derivative of the function at that point. From: Beginner Calculus Learn more: Explore all courses:
πŸ“ Riesz Representation Theorem Every continuous linear functional $f$ on a Hilbert space $H$ has the form $f(v) = \\langle v, u \\rangle$ for a unique $u \\in H$. Proof: If $f = 0$, take $u = 0$. Otherwise, $\\ker f$ is a closed hyperplane. Take $u_0 \\perp \\ker f$ with $f(u_0) = 1$. Set $u = \\overline{f(u_0)/\\|u_0\\|^2} \\cdot u_0$. From: adv_linalg Learn more: Explore all courses:
πŸ“– Composition of Transformations Let $U, V, W$ be sets. Let $T: U \\to V$ and $S: V \\to W$. The \\textbf{composition} $ST$ is the function $ST: U \\to W$ defined by $(ST)(x) = S[T(x)]$ for every $x$ in $U$. From: calc2 Learn more: Explore all courses:
πŸ“ 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:
πŸ“ 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:
πŸ“ 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:
πŸ’‘ 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:
πŸ“– 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:
πŸ’‘ 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:
πŸ“– 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:
πŸ“ 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:
πŸ“ 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:
πŸ“ Integration of sinΒ²(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:
↑