# EquationsDefiningFunctions

## Equations Defining Functions (Not Implicit)

This PG code shows how to check student answers that are equations that define functions. If an equation defines a function, it is much more reliable to use the this method of answer evaluation (via `parserAssignment.pl`) than the implicit equation method (via `parserImplicitEquation.pl`).

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

Initialization: We need to include the macro file `parserAssignment.pl`.

```Context("Numeric")->variables->are(x=>"Real",y=>"Real");
parser::Assignment->Allow;
parser::Assignment->Function("f");

\$eqn = Formula("y=5x+2");
\$f = Formula("f(x)=5x+2");
```

Setup: We must allow assignment, and declare any function names we wish to use. For more details and examples in other MathObjects contexts, see parserAssignment.pl.html

```BEGIN_TEXT
Enter \( y = 5x+2 \) \{ ans_rule(20) \}
\$BR
Enter \( f(x) = 5x+2 \) \{ ans_rule(20) \}
END_TEXT
```

Main Text: The problem text section of the file is as we'd expect.

```ANS( \$eqn->cmp() );
ANS( \$f->cmp() );

ENDDOCUMENT();
```