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Coordinate systems in 3D
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MihailKovachev committed Jan 22, 2025
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32 changes: 32 additions & 0 deletions vault/Mathematics/Algebra/Inequalities/Logarithmic Inequalities.md
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>[!DEFINITION] Definition: Logarithmic Inequality
>
>A **(real) logarithmic inequality** is an [inequality](Inequality.md) which contains variables as part of the base or the argument of a logarithm.
>
>[!ALGORITHM]- Algorithm: Solving Inequalities of the Form $\log_a f(x) \gt \log_a g(x)$
>
>We are given the following inequality:
>
>$$
>\log_a f(x) \gt \log_a g(x)
>$$
>
>Solutions:
>- If $0 \lt a \lt 1$, then $\begin{cases}f(x) \lt g(x) \\ f(x) \gt 0\end{cases}$
>- If $a \gt 1$, then $\begin{cases}f(x) \gt g(x) \\ g(x) \gt 0\end{cases}$
>
>[!ALGORITHM]- Algorithm: Solving Inequalities of the Form $\log_{b(x)}f(x) \ge \log_{b(x)} g(x)$
>
>We are given the following inequality:
>
>$$
>\log_{b(x)}f(x) \ge \log_{b(x)} g(x)
>$$
>
>Solutions:
>
>$$
>\begin{cases}0 \lt b(x) \lt 1 \\ f(x) \le g(x) \\ f(x) \gt 0\end{cases} \qquad \bigcup \qquad \begin{cases}b(x) \gt 1 \\ f(x) \ge g(x) \\ g(x) \gt 0 \end{cases}
>$$
>
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>[!ALGORITHM] Algorithm: Solving Inequalities of the Form $\sin x \lt c, \sin x \le c, \sin x \ge c, \sin x \gt c$
>
>>[!ALGORITHM] Algorithm: Solving Inequalities of the Form $\sin x \lt c$ or $\sin x \le c$
>>
>>We are given a [trigonometric inequality](Trigonometric%20Inequality.md) of the following form.
>>
>>$$
>>\sin x \lt c
>>$$
>>
>>Solutions:
>>- If $c \le -1$, then $x \in \varnothing$.
>>-
>>
>[!ALGORITHM]- Algorithm: Solving Inequalities of the Form $\sin x \lt c$ and $\sin x \le c$
>
>We are given a [trigonometric inequality](Trigonometric%20Inequality.md) of the following form.
>
>$$
>\sin x \lt c
>$$
>
>Solutions:
>
>$$
>x \in \bigcup_{k \in \mathbb{Z} \left(-\pi - \alpha_0 + 2k\pi; \alpha_0 + 2k\pi \right)
>$$
>
>[!ALGORITHM]- Algorithm: Solving Inequalities of the Form $\cos x \lt c$ and $\cos x \le c$
>
>We are given a [trigonometric inequality](Trigonometric%20Inequality.md) of the following form.
>
>$$
>\cos x \lt c
>$$
>
>Solutions:
>- If $c \le -1$, then $x \in \varnothing$.
>
>[!ALGORITHM]- Algorithm: Solving Inequalities of the Form $\tan x \gt c$ and $\tan x \ge c$
>
>We are given a [trigonometric inequality](Trigonometric%20Inequality.md) of the following form.
>
>$$
>\tan x \gt c
>$$
>
>Solutions:
>
>$$
>x \in \bigcup_{k \in \mathbb{Z}} \left(\alpha_0 + k\pi; \frac{\pi}{2}+k\pi \right)
>$$
>
>[!ALGORITHM]- Algorithm: Solving Inequalities of the Form $\cot x \lt c$ and $\cot x \le c$
>
>We are given a [trigonometric inequality](Trigonometric%20Inequality.md) of the following form.
>
>$$
>\cot x \lt c
>$$
>
>Solutions:
>- If $c \le -1$, then $x \in \varnothing$.
>-
>
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>[!THEOREM]- Theorem: Cartesian $\leftrightarrow$ Polar
>
>If $\mathbf{p} \in \mathbb{R}^2$ has [Cartesian coordinates](Cartesian%20Coordinate%20System.md) $(x,y)$, then its [polar coordinates](Polar%20Coordinate%20System.md) $(r, \theta)$ are:
>
>- Using the convention $r \ge 0$ and $\theta \in (-\pi; \pi]$:
>
>$$
>\begin{align*}
>r &= \sqrt{x^2 + y^2} \\
>
>\theta &=
>
>\begin{cases}
>
>\arctan \left( \frac{y}{x} \right) \qquad \qquad \text{if } x \gt 0 \\
>
>\arctan \left( \frac{y}{x} \right) + \pi \qquad \text{ if } x \lt 0, y \ge 0 \\
>
>\arctan \left( \frac{y}{x} \right) - \pi \qquad \text{ if } x \lt 0, y \lt 0 \\
>
>\frac{\pi}{2} \qquad \qquad \qquad \qquad \text{if } x = 0, y \gt 0 \\
>
>-\frac{\pi}{2} \qquad \qquad \qquad \, \, \, \, \, \, \text{ if } x = 0, y \lt 0 \\
>
>0 \qquad \qquad \qquad \qquad \, \text{ if } x = y = 0
>
>\end{cases}
>
>\end{align*}
>$$
>
>- Using the convention $r \ge 0$ and $\theta \in [0; 2\pi)$:
>
>$$
>\begin{align*}
>
>r &= \sqrt{x^2 + y^2} \\
>
>\theta &=
>
>\begin{cases}
>
>\arccos \frac{x}{\sqrt{x^2 + y^2}} \qquad \qquad \text{ if } y > 0 \\
>
>2\pi - \arccos \frac{x}{\sqrt{x^2 + y^2}} \qquad \text{if } y < 0 \\
>
>0 \qquad \qquad \qquad \qquad \hphantom{,,,,} \text{if } y = 0, x \ge 0 \\
>
>\pi \qquad \qquad \qquad \qquad \hphantom{,,,,} \text{if } y = 0, x \lt 0
>
>\end{cases}
>
>\end{align*}
>$$
>
>If $\mathbf{p} \in \mathbb{R}^2$ has [polar coordinates](Polar%20Coordinate%20System.md) $(r, \theta)$, then its [Cartesian coordinates](Cartesian%20Coordinate%20System.md) $(x,y)$ are
>
>$$
>\begin{align*}
>
>x &= r \cos \theta \\
>
>y &= r \sin \theta
>
>\end{align*}
>$$
>
>>[!PROOF]-
>>
>>TODO
>>
>
>[!THEOREM]- Theorem: Cartesian $\leftrightarrow$ Spherical
>
>If $\mathbf{p} \in \mathbb{R}^3$ has [Cartesian coordinates](Cartesian%20Coordinate%20System.md) $(x,y,z)$, then its [spherical coordinates](Spherical%20Coordinate%20System.md) $(r, \theta, \phi)$ are:
>
>- Using the convention $r \ge 0$, $\theta \in [0; \pi]$ and $\phi \in (-\pi; \pi]$:
>
>$$
>\begin{align*}
>
>r &= \sqrt{x^2 + y^2 + z^2} \\
>
>\theta &=
>\begin{cases}
>
>0 \qquad \qquad \qquad \hphantom{,,,,,} \text{if } x = y = z = 0 \\
>
>\arccos \frac{z}{\sqrt{x^2 + y^2 + z^2}} \hphantom{,,,,} \text{otherwise }
>
>\end{cases} \\
>
>\phi &=
>
>\begin{cases}
>
>\arctan \left( \frac{y}{x} \right) \qquad \qquad \text{if } x \gt 0 \\
>
>\arctan \left( \frac{y}{x} \right) + \pi \qquad \text{ if } x \lt 0, y \ge 0 \\
>
>\arctan \left( \frac{y}{x} \right) - \pi \qquad \text{ if } x \lt 0, y \lt 0 \\
>
>\frac{\pi}{2} \qquad \qquad \qquad \qquad \text{if } x = 0, y \gt 0 \\
>
>-\frac{\pi}{2} \qquad \qquad \qquad \, \, \, \, \, \, \text{ if } x = 0, y \lt 0 \\
>
>0 \qquad \qquad \qquad \qquad \, \text{ if } x = y = 0
>
>\end{cases}
>
>\end{align*}
>$$
>
>- Using the convention $r \ge 0$, $\theta \in [0; \pi]$ and $\phi \in [0; 2\pi)$:
>
>$$
>\begin{align*}
>
>r &= \sqrt{x^2 + y^2 + z^2} \\
>
>\theta &=
>\begin{cases}
>
>0 \qquad \qquad \qquad \hphantom{,,,,,} \text{if } x = y = z = 0 \\
>
>\arccos \frac{z}{\sqrt{x^2 + y^2 + z^2}} \hphantom{,,,,} \text{otherwise }
>
>\end{cases} \\
>
>\phi &=
>
>\begin{cases}
>
>\arccos \frac{x}{\sqrt{x^2 + y^2}} \qquad \qquad \text{ if } y > 0 \\
>
>2\pi - \arccos \frac{x}{\sqrt{x^2 + y^2}} \qquad \text{if } y < 0 \\
>
>0 \qquad \qquad \qquad \qquad \hphantom{,,,,} \text{if } y = 0, x \ge 0 \\
>
>\pi \qquad \qquad \qquad \qquad \hphantom{,,,,} \text{if } y = 0, x \lt 0
>
>\end{cases}
>
>\end{align*}
>$$
>
>If $\mathbf{p} \in \mathbb{R}^3$ has [spherical coordinates](Spherical%20Coordinate%20System.md) $(r, \theta, \phi)$, then its [Cartesian coordinates](Cartesian%20Coordinate%20System.md) $(x,y,z)$ are
>
>$$
>\begin{align*}
>
>x &= r \sin \theta \cos \phi \\
>
>y &= r \sin \theta \sin \phi \\
>
>z &= r \cos \theta
>
>\end{align*}
>$$
>
>>[!PROOF]-
>>
>>TODO
>>
>
>[!THEOREM]- Theorem: Cartesian $\leftrightarrow$ Cylindrical
>
>If $\mathbf{p} \in \mathbb{R}^3$ has [Cartesian coordinates](Cartesian%20Coordinate%20System.md) $(x,y,z)$, then its [Cylindrical coordinates](Cylindrical%20Coordinate%20System.md) $(\rho, \phi, z)$ are:
>
>- Using the convention $\rho \ge 0$ and $\phi \in (-\pi; \pi]$:
>
>$$
>\begin{align*}
>
>\rho &= \sqrt{x^2 + y^2} \\
>
>\phi &=
>
>\begin{cases}
>
>\arctan \left( \frac{y}{x} \right) \qquad \qquad \text{if } x \gt 0 \\
>
>\arctan \left( \frac{y}{x} \right) + \pi \qquad \text{ if } x \lt 0, y \ge 0 \\
>
>\arctan \left( \frac{y}{x} \right) - \pi \qquad \text{ if } x \lt 0, y \lt 0 \\
>
>\frac{\pi}{2} \qquad \qquad \qquad \qquad \text{if } x = 0, y \gt 0 \\
>
>-\frac{\pi}{2} \qquad \qquad \qquad \, \, \, \, \, \, \text{ if } x = 0, y \lt 0 \\
>
>0 \qquad \qquad \qquad \qquad \, \text{ if } x = y = 0
>
>\end{cases} \\
>
>z &= z
>
>\end{align*}
>$$
>
>- Using the convention $\rho \ge 0$ and $\phi \in [0; 2\pi)$:
>
>$$
>\begin{align*}
>
>\rho &= \sqrt{x^2 + y^2} \\
>
>\phi &=
>
>\begin{cases}
>
>\arccos \frac{x}{\sqrt{x^2 + y^2}} \qquad \qquad \text{ if } y > 0 \\
>
>2\pi - \arccos \frac{x}{\sqrt{x^2 + y^2}} \qquad \text{if } y < 0 \\
>
>0 \qquad \qquad \qquad \qquad \hphantom{,,,,} \text{if } y = 0, x \ge 0 \\
>
>\pi \qquad \qquad \qquad \qquad \hphantom{,,,,} \text{if } y = 0, x \lt 0
>
>\end{cases} \\
>
>z &= z
>
>\end{align*}
>$$
>
>If $\mathbf{p} \in \mathbb{R}^3$ has [Cylindrical coordinates](Cylindrical%20Coordinate%20System.md) $(\rho, \phi, z)$, then its [Cartesian coordinates](Cartesian%20Coordinate%20System.md) $(x,y,z)$ are
>
>$$
>\begin{align*}
>
>x &= \rho \cos \phi \\
>
>y &= \rho \sin \phi \\
>
>z &= z
>
>\end{align*}
>$$
>
>>[!PROOF]-
>>
>>TODO
>>
>
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