Matt submits the above, and Matt writes, “I think it’s especially interesting that this student left the mistake on the board even though she had found the correct solutions by graphing in Desmos. I’m not really sure if she did half of forty, or sqrt 4 and then stuck a zero on it (she wasn’t sure either).”

I vote for “half of 40.” You?

## 4 replies on “Completing the Square, II”

I’d absolutely vote half of forty; the “exponents are multiplication and roots are division” is pretty typical (a.k.a. ‘it’s supposed to get smaller, so…’) I work pretty hard at trying to get that radical thing to take on a life of its own so that it means something.

right, well, she hadn’t actually found the correct solution. Only one of the two solutions shown on the graph is correct. I found that interesting, too.

ps: i vote for as the likelier thinko here.

and confidently predict that its author will go on to munge the quadratic formula *many* times… without much useful interference… or even big red X’s, most of the time i suppose… from any more competent individuals that happen to witness said munging. they probably won’t understand the “plus-minus” bit any better than they do the radical. and of course, their “cancelling” chops will probably lack that special something that comes only with having some idea what the devil one is trying to accomplish in the first place. when in doubt, scribble some damn nonsense and hand it in. we’re all saved by the bell eventually, right?