Update the sample problem demonstrating custom graphtool checker ussage.

Author: drgrice1

tutorial/sample-problems/Algebra/GraphToolCustomChecker.pg

@@ -86,18 +86,6 @@ $gt = GraphTool("{circle, solid, ($h, $k), ($h + $r, $k)}")->with(
             my @errors;
             my $count = 1;
 
-            # Get the center and point that define the correct circle and
-            # compute the square of the radius.
-            my ($cx, $cy) = $correct->[0]->extract(3)->value;
-            my ($px, $py) = $correct->[0]->extract(4)->value;
-            my $r_squared = ($cx - $px)**2 + ($cy - $py)**2;
-
-            my $pointOnCircle = sub {
-                my $point = shift;
-                my ($x, $y) = $point->value;
-                return ($x - $cx)**2 + ($y - $cy)**2 == $r_squared;
-            };
-
             # Iterate through the objects the student graphed and check to
             # see if each is the correct circle.
             for (@$student) {
@@ -107,12 +95,8 @@ $gt = GraphTool("{circle, solid, ($h, $k), ($h + $r, $k)}")->with(
                 # type as the correct object type (a circle in this case),
                 # has the same solid or dashed status, has the same center, and
                 # if the other point graphed is on the circle.
-                if ($_->extract(1) eq $correct->[0]->extract(1)
-                    && $_->extract(2) eq $correct->[0]->extract(2)
-                    && $_->extract(3) == $correct->[0]->extract(3)
-                    && $pointOnCircle->($_->extract(4)))
-                {
-                    $score += 1;
+                if ($correct->[0] == $_) {
+                    ++$score;
                     next;
                 }
 
@@ -124,7 +108,13 @@ $gt = GraphTool("{circle, solid, ($h, $k), ($h + $r, $k)}")->with(
                     next;
                 }
 
-                if ($_->extract(2) ne $correct->[0]->extract(2)) {
+                # Calling $correct->[0]->cmp($_, 1) does a "fuzzy" comparison.
+                # This is the same as $correct->[0] == $_ except that it ignores
+                # the solid or dashed status and only checks the center point
+                # and radius, i.e., that the circles are the same.
+                if ($correct->[0]->cmp($_, 1)
+                    && $_->extract(2) ne $correct->[0]->extract(2))
+                {
                     push(@errors,
                         "The $nth object graphed should be a "
                             . $correct->[0]->extract(2)