PG problem file Explanation
```DOCUMENT();
"PGstandard.pl",
"MathObjects.pl",
"parserImplicitPlane.pl",
);
TEXT(beginproblem());
```

Initialization: We need to include the macros file `AnswerFormatHelp.pl`.

```Context("ImplicitPlane")->variables->are(x=>"Real",y=>"Real");

```

Setup: By declaring there are only two variables, `ImplicitPlane` will address objects as lines rather than planes.

```BEGIN_TEXT
Enter an equation for a line through the points
\( (0,2) \) and \( (2,0) \).
\$BR
\$BR
\{ ans_rule(20) \}
END_TEXT
```

Main Text: We use `AnswerFormatHelp("equations")` to generate a link to an html help file with link text `help (equations)`. The html help files are specifically designed to help students figure out the correct syntax for their answer, as well as common mistakes to avoid. We recommend placing a help link immediately after each answer blank in a problem, especially if there are different types of answers. Currently, help files are available for

• angles
• decimals
• exponents
• formulas
• fractions
• inequalities
• intervals
• logarithms
• limits
• numbers
• points
• syntax
• units
• vectors

It is possible to change the link text to `help entering equations` by including a second argument to the routine:

```\{ AnswerFormatHelp("equations","help entering equations") \}
```

It is possible to provide a link to an external help file using `\{ htmlLink("http://someplace.edu/help.html") \}`. We do not recommend this as it requires external files be maintained and links not become broken (especially when the server changes or moves). Instead of using a link to an external help file, use the method described at the bottom of this page.

```\$showPartialCorrectAnswers = 1;

ENDDOCUMENT();
```

Instead of using a link to an external file, use the following:

```HEADER_TEXT(<<END_HEADER_TEXT);
<script type="text/javascript">
<!--
function openhelpCustom1() {
OpenWindow.document.write("<title>Help With Something</title>")
OpenWindow.document.write("<body bgcolor='#ffffff'>")
OpenWindow.document.write("<center><h2>Help With Something</h2></center>")
OpenWindow.document.write("<ul>")
OpenWindow.document.write("</ul>")
OpenWindow.document.write("</body>")
OpenWindow.document.write("</html>")
OpenWindow.document.close()
self.name="main"
if (window.focus) {OpenWindow.focus()}
return false;
}
-->
</script>

BEGIN_TEXT