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).

```\$showPartialCorrectAnswers = 1;

ENDDOCUMENT();
```