# NAME

parserSolutionFor.pl - An answer checker that checks if a student's answer satisifies an implicit equation.

# DESCRIPTION

This is a Parser class that implements an answer checker that checks if a student's answer satisfies an implicit equation. We define a SolutionFor object class that lets you specify an equality that the student answer must satisfy, and a point that DOES satify the equation. The overloaded == operator will check if a given point satisfies the given equality.

Use SolutionFor(equality,point[,options]) to create a SolutionFor object. The equality is a Formula object containing an equality, or a string representing such a formula, and the point is a Point object or string containing a point that satisfies the equation (to be used as the correct answer when the student asks to see the answers).

The variables to use are declared in the Context in the usual way, and the coordinates of the student point will be considered to be in alphabetical order. You can override this by supplying the vars=>[...] option, where you specify the variable names in the order you want the student to give them. E.g., vars=>['y','x'] will make the student answer represent the point (y,x) rather than the default (x,y).

Usage examples:

```        Context("Vector")->variables->are(x=>'Real',y=>'Real');
\$f = SolutionFor("x^2 = cos(y)","(1,0)");
\$f = SolutionFor("x^2 - y = 0",[2,4]);
\$f = SolutionFor("x^2 - y = 0",Point(4,2),vars=>['y','x']);```

Then use

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

to get the answer checker for \$f.

You can use \$f->{f} to get the Formula object for the equality used in the object, and \$f->f(point) to determine if the given point is a solution to the equality or not. For example, if you want to include the TeX version of a formula within the text of a problem, you can use:

```        Context()->texStrings;
BEGIN_TEXT
A solution to \(\$f->{f}\) is \((x,y)\) = \{ans_rule(30)\}.
END_TEXT
Context()->normalStrings;
ANS(\$f->cmp);```