new-tag A new tagtrig-equation was created by Harish Chandra Rajpoot. (The tag-info was left empty.) I am not sure the tag is needed - since there already is trigonometry.
Recently I worked on a problem where I had to solve $$\cos(3x)+\cos(x)=0$$
When I tried calculating it by evaluating $x$, $x=2nπ+\dfrac{\pi}{4}$, $x=2n\pi-\dfrac{\pi}{4}$, or $x=2n\pi+\dfrac{\pi}{2}$ was the solution I reached.
Unfortunately, it was apparently wrong. Is there another way to solv...
Addition to the tag-excerpt: "This includes logical compactness." Addition to the tag-wiki: "This tag may also be used for questions about logical compactness, such as the compactness theorem."
The current revision of the tag-excerpt:
> The compactness tag is for questions about compactness and its many variants (e.g. sequential compactness, countable compactness) as well locally compact spaces; compactifications (e.g. one-point, Stone-Čech) and other topics closely related to compactness. This includes logical compactness.
The current revision of the tag-wiki:
> Compactness is a topological property. We say that a topological space $X$ is compact if whenever we cover $X$ by a collection of open sets we can find a finite number of open sets from the collection which cover $X$. For example, $[0,1]$ is a compact subspace of $\mathbb{R}$, but $(0,1)$ and $\mathbb{R}$ are not.
> We say that a space $X$ is sequentially compact if every sequence has a convergent subsequence. These properties are equivalent for metric space, although neither implies the other in general.
> This tag may also be used for questions about logical compactness, such as the compactness theorem.
