## WeBWorK Problems

### Checking Vector Functions

by Murphy Waggoner -
Number of replies: 2
None of my students were getting the answer correct for this problem:  webwork-open-problem-library/OpenProblemLibrary/FortLewis/Calc3/17-2-Motion-velocity/HGM4-17-2-30-Motion-velocity-acceleration.pg.

I think the issue was that the solution was a vector function

L(t) = r_0 + v_0(t - t_0)       (1)

But the students were all using what they knew from a previous section that the equation of a line in space is of the form

L(t) = r_0 + D*(t)                (2)

And the problem did not say that the value of t at r_0 needed to be the same for the curve r(t) and the tangent line L(t).

I am wondering if there is a vector function checker out there that would accept (2) as an answer when the formula for the answer is (1)

### Re: Checking Vector Functions

by Paul Pearson -
Hi Murphy,

The problem text clearly states that the students should use the original time parameter t, which necessitates having an answer with (t-t_0) in it.

"Find a vector parametric equation for the position of the particle (in terms of the original parameter $$t$$) as it moves along this tangent line."

Changing the line

	$T = Formula("(t -$b)") -> reduce;
to
	\$T = Formula("t");
should make your students' previous answer correct.  Of course, you'd want to change the problem text, too.

Best regards,

Paul Pearson

There is a ParametricLine() object in the parserParametricLine.pl file that compares parametric lines and will accept any version of the same line (different starting points, different but parallel vectors). Perhaps that could be used here. I'm not sure what your D value is (it doesn't seem to be in the problem itself), so you might need to add that into the context as a vector-valued constant.