## WeBWorK Problems

### Interval notation for the students ### Interval notation for the students

by Valerio De Angelis -
Number of replies: 0
I would like the students to be able to always use the same notation for infinity in their answers, that is, I=infinity, -I=-Infinity. I know how to do this when the answer is just I or -I, but I am not able to get the answer evaluator to accept
an interval in the form (-I,4] for example. In the problem below, the answer has to be entered as (-Infinity,2) or (-inf,2), but I would like the students to be able to enter (-I,2). Is this possible?

DOCUMENT();

"MathObjects.pl",
"PGgraphmacros.pl",
"PGML.pl",
"PGcourse.pl"
);

TEXT(beginproblem());

$showPartialCorrectAnswers = 1;$refreshCachedImages=1;

Context("Point");

$pixels=400; #create the canvas$gr=init_graph(-10,-10,10,10,# xmin,ymin, xmax, ymax
axes=>[0,0],grid=>[20,20],size=>[$pixels,$pixels]);
$gr->lb('reset'); #remove default labels # axes labels$gr->lb(new Label(9.5,0,'x','black','center','bottom'));
$gr->lb(new Label(0.1,9.5,'y','black','left','middle')); foreach my$i (-10..10){
$gr->lb( new Label($i,0,$i,'black','center','top'));$gr->lb( new Label(-0.1,$i,$i,'black','right','middle'));
}
#plot a function
$e=0.1;$t1=random(2,2,1);
$t11=$t1-$e;$t12=$t1+$e;
$t2=$t1+2;
$t20=$t2-$e;$t21=$t2+2*$e;
$t3=$t2+4;
$t30=$t3-$e;$t31=$t3+$e/4;
$t22=$t2+2;

$L1=Formula("-1/(x-$t1)+2");
$L2=Formula("7/2");$L3=Formula("3*sin(3*(x-$t3))+7/2");$a=3*sin(3*(9-$t3))+7/2; add_functions($gr, "$L1 for x in <-10,$t11> using color:blue and weight:2",
"$L1 for x in <$t12,$t20> using color:blue and weight:2", "$L2 for x in <$t21,$t30> using color:blue and weight:2",
"$L3 for x in <$t31,9> using color:blue and weight:2");

$gr->stamps( new Circle($t2,2.5,4,'blue','blue'));
$gr->stamps( new Circle($t2,1.5,4,'blue',''));
$gr->stamps( new Circle($t2,3.5,4,'blue',''));
$gr->stamps( new Circle($t3,1,4,'blue','blue'));

$gr->stamps( new Circle($t3,3.5,4,'blue',''));

$gr->stamps( new Circle(9,$a,4,'blue','blue'));

$ans=Interval("(-inf,$t1)");

BEGIN_PGML
The graph of [ f(x)] is shown in the picture.

>>[@image(insertGraph($gr),width=>$pixels, height=>$pixels, tex_size=>900) @]*<< The function is continuous on [_____]{$ans}
END_PGML

BEGIN_PGML_SOLUTION
*SOLUTION*
END_PGML_SOLUTION

ENDDOCUMENT();