Any way to solve parametric inequations?
09-14-2021, 10:58 PM (This post was last modified: 09-15-2021 02:30 AM by jte.)
Post: #13
 jte Member Posts: 156 Joined: Feb 2014
RE: Any way to solve parametric inequations?
As a human, trying to understand xy/(x+y)^2≤0, for real x and y, one approach would be to handle (0,0) separately first and then look at the punctured plane, R^2\{(0,0)}.

… so… doing that…

Realizing that (x,y) is a solution iff (kx,ky) is, for positive k, lets us change our focus from R^2\{(0,0)} to the unit circle (each point on the circle is then a representative for an open ray from the origin), or — better yet — for nonzero k, which lets us consider half of a unit circle (each point on the half circle is then a representative for a punctured line through the origin).

If we pick the northeast half circle (x^2+y^2=1 s.t. y≥-x … although we only need one of the half circle’s end points), we can then exploit the symmetry that (x,y) is a solution iff (y,x) is to fold the half circle over y=x and consider just the upper quarter of a unit circle, x^2+y^2=1 s.t. y≥.5sqrt(2) (now each point is a representative of two punctured lines, or we could unfold our solution later before expanding back to the punctured plane). Looking at xy/(x+y)^2, one can see where the solutions are (from the left endpoint, not including it, to the halfway point, including it).

I’m not quite sure how this relates to automated solving / automated presentation of results. But considering symmetries etc. is certainly part of mathematics.
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 Messages In This Thread Any way to solve parametric inequations? - dah145 - 09-04-2021, 02:49 AM RE: Any way to solve parametric inequations? - jte - 09-05-2021, 04:30 PM RE: Any way to solve parametric inequations? - dah145 - 09-07-2021, 09:48 PM RE: Any way to solve parametric inequations? - jte - 09-12-2021, 11:42 PM RE: Any way to solve parametric inequations? - parisse - 09-13-2021, 04:49 PM RE: Any way to solve parametric inequations? - roadrunner - 09-13-2021, 06:39 PM RE: Any way to solve parametric inequations? - Albert Chan - 09-13-2021, 07:42 PM RE: Any way to solve parametric inequations? - jte - 09-13-2021, 09:33 PM RE: Any way to solve parametric inequations? - Albert Chan - 09-14-2021, 12:55 AM RE: Any way to solve parametric inequations? - jte - 09-14-2021, 05:13 AM RE: Any way to solve parametric inequations? - Albert Chan - 09-14-2021, 09:35 AM RE: Any way to solve parametric inequations? - Albert Chan - 09-14-2021, 10:23 AM RE: Any way to solve parametric inequations? - jte - 09-14-2021 10:58 PM RE: Any way to solve parametric inequations? - parisse - 09-15-2021, 04:53 AM

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