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If $xy > 0$, then $x$ and $y$ are [insert fancy smart term for same sign]

Does "sign parity" work here?

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    ...$b^2-4ac$ is called the discriminant of $ax^2+bx+c$, though I personally didn't know this till after I'd seen hundreds of quadratics.2012-04-05

3 Answers 3

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A quick search in Google Books gives the following quote:

[..] Hence, if $\Delta_{r-1}$ and $\Delta_r$ are of opposite signs, $\Delta_{r+1}$ and $\Delta_{r+2}$ are of the same sign as $\Delta_r$ [..]

You can't be smarter than H. S. M. Coxeter!

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    ...or you could say they are "of like sign"...2012-04-03
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If $x$ and $y$ are real numbers, then the followings are equivalent.

  • $xy>0$.
  • $x$ and $y$ are both nonzero, and cannot have differing signs.
  • The closed line segment connecting $x$ and $y$ does not contain $0$.
  • One can go from $x$ to $y$ without ever touching $0$.
  • The intervals $[x,y]$ and $[-x,-y]$ have no common point.
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I agree with user2468. Usually this is stated $x$ and $y$ have the same sign. sgn($x$)=sgn($y$) could also be used. [Weisstein, Eric W. "Sign." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/Sign.html]

Also "sign parity" would be confusing since "parity" is used to refer to even or oddness.