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Matrix multiplication: is C(AB) the same as (CA)B?
I would like to show that $(\mathbf{A} \mathbf{B})^{-1} = \mathbf{B}^{-1} \mathbf{A}^{-1}$, where $\mathbf{A}$ and $\mathbf{B}$ are $N \times N$ square ma...
Apr 10, 2026
Archive: News
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I want to get good at math, any good book suggestions? [closed]
I have never been good at math. In my senior year I failed algebra 2 in the first semester because the teacher would refuse to show me how to solve proble...
Apr 10, 2026
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Null sets in $\mathbb{R}$ and definition of Algebra of subsets of $\mathbb{R}$
The general set theory claims that there exists a set which has no members. From the point of view of $\mathbb{R}$ what are null sets? More specifically w...
Apr 10, 2026
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Find $k$ so that the following function is constant on any interval
$$f(x)= \begin{cases} x^2 + k & \text{if } x \leq 5 \\ k x\ &\text{if } x > 5 \end{cases} $$ I've seen where you set $x=5$ and plug in, bu...
Apr 10, 2026
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What is the meaning of a small o in between function names? i.e (f o g)
I am helping with homework. I am stumped here - What is the meaning of the small round circle, or small "o" in question 19 (that I underlined) and questio...
Apr 10, 2026
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First 10-digit prime in consecutive digits of e
Problem. What is the first $10$-digit prime in consecutive digits of $e$. For those of you who don't know, in 2004 the answer produced a URL to a Goo...
Apr 10, 2026
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How do I differentiate polynomials
can someone show me how to differentiate stuff like x + 2 and I've never did this before and I use the most god awful textbook imaginable. Much thanks
Apr 10, 2026
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An equation to map values from one range to another
I need a formula (preferably something I can write with JavaScript, so simple arithmetic) that will map my value that is between 0.5 and 1, to a new value...
Apr 10, 2026
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What does it mean to take the gradient of a vector field?
What does it mean to take the gradient of a vector field? $\nabla \vec{v}(x,y,z)$? I only understand what it means to take the grad of a scalar field.
Apr 10, 2026
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How to find vertices of square in complex numbers
Given a square with vertices: $\sqrt3+i,-1+i\sqrt3,-i-\sqrt3,1-i\sqrt3$ So that a circle that is centered in the origin is blocking the square. My questio...
Apr 10, 2026
