Toronto Math Forum
MAT2442014F => MAT244 MathLectures => Topic started by: Matthew Pick on November 13, 2014, 12:06:14 AM

Today while writing the quiz, I was attempting to figure out question 2 with little avail.
Grasping at straws  I decided to enter in 4 points into the formula for the derivative for x' (the points were (1,0), (1,0), (0,1), (1,0) )
I noticed that the slopes for (1,0) and (1,0) were negative inverses.
The same was true for the slopes of (0,1) and (0,1).
I guessed that this implied that each of the pairs of points were on circles (ellipses? in any case it was a centre..). Upon checking the answers on the forum this evening, this seems to be true.
Is this always the case? I realize that this is not a particularly rigorous way of solving, but it seems like it might be a good method to check answers if anyone, like I am, is prone to computational mistakes...

Why you just don't learn a very simple criteria for the center or focus: if the topright element of $2\times 2$ matrix is $>0$ the orientation is clockwise; otherwi\se it is counterclockwise