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Wrong Answer?

asked 2014-08-19 23:46:36 +0100

When I ask Sage to solve a simple rational inequality it occasionally gives a wrong answer. For example, $$ \frac{x^2 - 9 }{x-3} \geq 0$$ is satisfied when $x \geq -3$ except at $x=3$, but Sage just gives $x \geq -3$. Here's the code I am using:

sage: solve((x^2-9)/(x-3) >= 0,x)
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answered 2014-08-20 14:50:12 +0100

kcrisman gravatar image

updated 2014-08-21 22:20:10 +0100

This is in Maxima.

Maxima 5.33.0
using Lisp ECL 12.12.1
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) load("solve_rat_ineq"); 
(%o1) /Users/.../sage/local/share/maxima/5.33.0/share/solve\
(%i2) solve_rat_ineq((x^2-9)/(x-3) >= 0);
(%o2)                            [[x >= - 3]]

That said, Maxima (and Sage and lots of other things) do simplify x^2/x to be just x, so I am not 100% sure it's not intended behavior. Anyway, I agree it would be better to not have the 3, so I've reported it at Maxima bug 2804.

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Asked: 2014-08-19 23:46:36 +0100

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Last updated: Aug 21 '14