This is a first draft of a TikZ picture illustraing this classical formula to be used for math help channels.

Adding `\caption{for the picture}`

without “Figure 1:” requires
`\usepackage{caption}`

and wrapping with `\begin{figure}`

. It also possible to
use the primitive TeX command `\par`

, but it would be complicated to use that
with `standalone`

. In the previous post, the SVG picture from the LaTeX table
in an `article`

has too much useless whitespace around the table. I don’t
bother to learn other packages, as I need time for other more important stuff.

As a work around, I used `\node at (x,y) {node content}`

. Adding `[draw]`

before `{node content}`

gives a rectangular box enclosing the node.

The grid lines need to be drawn before the axes. I learnt the technique of
double `grid`

lines from the classic *TikZ pour l’impatitent*. The `[-latex]`

style comes from the LaTeX plugin in VS Code. I used `[pos=1.05]`

instead of
`[right]`

and `[above]`

to unify code the two axes. The graph of the staight
line is restricted by `\clip {TikZ command for a geomteric shape}`

, which is
restricted by `\begin{scope}`

and `\end{scope}`

.

```
\documentclass[tikz,border=2pt]{standalone}
\begin{document}
\begin{tikzpicture}
\coordinate (O) at (0,0);
\coordinate (L) at (-2.5,0);
\coordinate (R) at (2.5,0);
\coordinate (D) at (0,-2.5);
\coordinate (T) at (0,2.5);
\coordinate (A) at (1,0);
\coordinate (B) at (0,1.5);
\node at (0, 3.5) [draw] {
Equation of straight line in intercept form
};
\draw[help lines, step=0.1] (-2, -2) grid (2,2);
\draw[gray, line width=0.75, step=0.5] (-2, -2) grid (2,2);
\draw[-latex] (L) -- (R) node[pos=1.05] {$x$};
\draw[-latex] (D) -- (T) node[pos=1.05] {$y$};
\begin{scope}
\clip (-2.5,-2.5) rectangle (2.5,2.5);
\draw[thick] plot[domain=-3:3] (\x,{-1.5*\x/1 + 1.5});
\draw (A) node {$\times$} node[below left] {$a$};
\draw (B) node {$\times$} node[below left] {$b$};
\end{scope}
\node at (0,-4) [draw, align=center] {
$a = x\textrm{-intercept}$ \\
$b = y\textrm{-intercept}$ \\ [1ex]
$\displaystyle\frac{x}{a} + \frac{y}{b} = 1$
};
\end{tikzpicture}
\end{document}
```