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Task

References

Requirements

Katex math requirements

GOOD:

$$
\Phi(\mathbf r_1)=-G\int\frac{\rho(\mathbf r)}{|\mathbf r_1-\mathbf r|}d^3r_1
$$

$\ddot{\mathbf r}=-G(M+m)\frac{\mathbf r}{r^3}$

BAD:

$$\Phi(\mathbf r)
=-G\int\frac{\rho(\mathbf r')}{|\mathbf r-\mathbf r'|}d^3r'$$

GOOD:

\mathbf{r}

BAD:

\mathbf r

GOOD:

$$
\begin{cases}
\ddot{\mathbf{r}}_m=-GM\frac{\mathbf{r}}{r^3} \text{ (1)/m} \\
\ddot{\mathbf{r}}_M=+Gm\frac{\mathbf{r}}{r^3} \text{ (2)/M}
\end{cases}
$$

BAD:

$$
\ddot{\mathbf{r}}_m=-GM\frac{\mathbf{r}}{r^3} \text{ (1)/m} \\
\ddot{\mathbf{r}}_M=+Gm\frac{\mathbf{r}}{r^3} \text{ (2)/M}
$$

- Use symbolic language whenever possible

GOOD:

$$\exists a \in B$$


BAD:

There exists $a$ in $B$


- to emphasise multiple variables all have a value $a$, use , to separate the variables

GOOD:

$$ c_1, c_2, \cdots, c_n = 0. $$

BAD:

c_1 = c_2 = \cdots = c_n = 0.

IMPORTANT: think of reader

Show, don't tell

GOOD

== Mathematical definition ==

Let $V$ be a vector space over $\mathbb{F}$.

Map

$$
\begin{aligned}
\langle \cdot, \cdot \rangle : V \times V \to \mathbb{F}\\
\quad (u, v) \mapsto \langle u, v \rangle
\end{aligned}
$$

is an '''inner product''' on $V$ if 4 conditions are satisfied:

* '''Linearity in the 1st slot''': $\forall (u, v, w \in V, a \in \mathbb{F}), \langle u + v, w \rangle = \langle u, w \rangle + \langle v, w \rangle$ and $\langle au, v \rangle = a \langle u, v \rangle$
* '''Definiteness''': $\langle v, v \rangle = 0 \iff v = \vec 0$.
* '''Positivity''': $\forall v \in V, v \neq \vec 0, \langle v, v \rangle > 0$
* '''Conjugate symmetry''': $\forall u, v \in V, \langle u, v \rangle = \overline{\langle v, u \rangle}$.

<blockquote>
Recall:

$$\forall x\in\mathbb{R},\; x=\overline{x}$$

Hence, for real vector spaces, conjugate symmetry of an inner product becomes actual symmetry.
</blockquote>

<blockquote>
'''Warning''': confusingly, the convention in physics is often the exact opposite: an inner product is linear in the second slot and anti-linear in the first slot.
</blockquote>

BAD

Most laws of nature are stated as rules about how quantities change, so differential equations appear throughout science and engineering: the swinging of a pendulum, the cooling of a hot drink, the growth of a population, and the discharge of a capacitor are all described by differential equations. This article explains what a differential equation is and how equations are classified, then works through the most common exact methods of solution, each illustrated by a concrete numerical example that needs no background knowledge beyond school algebra. It treats '''ordinary differential equations''' (ODEs), in which the unknown function depends on a single independent variable, in the most detail, and gives shorter accounts of '''partial differential equations''' (PDEs) and of the numerical, series, and qualitative methods used when no exact formula exists.

(full of useless ramble and metacomments)

show complete derivation

discuss case-by-case

GOOD

pure algebra > real-world example

Do NOT duplicate

imitate style of the style examples