
Re: MIT Math Diagnostic for Physics Placement
Posted:
Oct 23, 2012 10:32 AM


Dave L. Renfro wrote (in part):
http://mathforum.org/kb/message.jspa?messageID=7910806
>> Problem B2: Instead of saying "Find all possible values of x which >> solve the equation x^4  13x^2 + 36 = 0", I would be less vague and >> explicitly ask for all complex solutions.
Robert Hansen wrote (in part):
http://mathforum.org/kb/message.jspa?messageID=7911198
> Doesn't that factor to (x^2  9)(x^2  4)? > x = +/3, +/2
Using "complex solutions" gives test takers making certain kinds of errors more rope to hang themselves with, although personally I consider something like x = +/ 3i, +/ 2i to be better than something like x = +/9, +/4, which in turn is better than something like x = +/13, +/36. Ideally, I'd want to see their work, but in the absence of that, for a total of 5 points for this problem, I might give 3 points for x = +/ 3i, +/ 2i and 12 points for x = +/9, +/4. Note that even x = +/9, +/4 suggests they correctly factored and they recognized there will be two pairs of solutions.
Dave L. Renfro

