Check out this kid’s explanation for why you end up with “+3x” from “-(-3x)”:

“You have -3x, so that’s three negatives, and then you have this other negative and that makes four…”

You can find this explanation at around 3:33 in the video below:

Exponents strike again!

(Or, maybe I misunderstood the kid’s explanation in the video? Lemme know if I did, please!)

Thanks to Jonathan for the submission.

  • Yeah, that’s part of the problem, but there’s so much wrong with this that my question is “Where do you start?” Let me give the background. The student was supposed to prove that a function is odd (show that -f(-x)=f(x) for those of us who haven’t had Precalculus in a while 🙂

    But yeah, I guess the explanation of why the 3x became positive with “4 negatives” really bothers me. Also, he seems to have distribute the negative out in front twice? But there’s definitely more in that short video that’s wrong–even starting at 3:33!