Here's the question you clicked on:
Hananana
A particle moves on a horizontal line as described by the equation s = t 3 −12t + 3 . a. When is the particle changing directions? b. When is the particle moving to the right and when is it moving to the left?
The particle changes direction when the velocity changes sign, so you would have to find out what specific times t, the function's velocity goes from neg->pos or pos->neg.
I already did it. But I was thinking about what to do with -2. I came up with 3(t-2)(t+2)=0 t=2, what shall I do with -2? There's no negative time -.-
Yup, if you can't have -2 but 2 is also an answer, the answer will be.....?
Yup. I haven't done the problem, but if that was your point of confusion, yes, if you have something for t that doesn't make sense (such as when t=0, or neg.) you can disregard it and only use the positive answer.
So that's it. I can do it now. Thanks