![Selecting 3 non-consecutive days of the week [duplicate]](https://edu.smbbmcl.edu.pk/uploads/selecting-3-non-consecutive-days-of-the-week-duplicate_720.jpg)
Selecting 3 non-consecutive days of the week [duplicate]
We need to find how many groups of $3$ days of the week there can be, given that no two days should be consecutive. The answer should be $7$, but I do not...
20 Apr 2026 1 READS
Archive: News
![Proving $\sum_{k=1}^{n}\cos\frac{2\pi k}{n}=0$ [duplicate]](https://edu.smbbmcl.edu.pk/uploads/proving-sum-k-1-n-cos-frac-2-pi-k-n-0-duplicate_720.jpg)
Proving $\sum_{k=1}^{n}\cos\frac{2\pi k}{n}=0$ [duplicate]
I want to prove that the below equation can be held. $$\sum_{ k=1 }^{ n } \cos\left(\frac{ 2 \pi k }{ n } \right) =0, \qquad n>1 $$ Firstly I tried to ...
20 Apr 2026 1 READS
Why is variable called "variable" in mathematics if in fact it's immutable?
I've never thought of this issue until recently when I've been using Haskell to build a substantial project. In Haskell (and functional programm...
20 Apr 2026 1 READS
Surface gradient and curvature
I am trying to get familiar with the surface gradient operator, i.e. $\nabla_S = (I-\mathbf{n}\mathbf{n})\cdot \nabla$, where $\mathbf{n}$ is the unit nor...
20 Apr 2026 1 READS
Changing signs of integration limits
When we reverse the limits and then change the signs of the limits of the definite integral $$\int\limits_{-R}^{-\epsilon}\frac{e^{ix}}{x}dx $$ the integr...
20 Apr 2026 1 READS
Shortcut to finding the square-root of a perfect-square?
I've been trying to speed up an algorithm where the most expensive operation is the square-root. However, I can often guarantee that the input value ...
20 Apr 2026 1 READS
The definition of continuous function in topology
I am self-studying general topology, and I am curious about the definition of the continuous function. I know that the definition derives from calculus, b...
20 Apr 2026 1 READS
Find a side of a triangle given other two sides and an angle
I have a really simple-looking question, but I have no clue how I can go about solving it? The question is Find the exact value of $x$ in the following di...
20 Apr 2026 1 READS
Interesting shapes using probability and discrete view of a problem
Suppose we have a circle of radius $r$, we show the distance between a point and the center of the circle by $d$. We then choose each point inside the cir...
20 Apr 2026 1 READS
What are the Differences Between a Matrix and a Tensor?
What is the difference between a matrix and a tensor? Or, what makes a tensor, a tensor? I know that a matrix is a table of values, right? But, a tensor?
20 Apr 2026 1 READS
