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I have a graphing calculator app (Graphing Calculator+) that only allows me to enter $x$ as a variable, but I need to graph $x = y^2 - 6$.

I haven't used a graphing calculator in awhile. Is this normal? If it is, is there some kind of a trick to graphing this equation?

Your help would be appreciated.

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    Maybe in parametric form? $x = t^2 - 6, y = t$ for $ -10< t< 10$2012-04-20
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    I use the app Desmos, It's free so I would recommend it @Subtle Array2016-01-03

3 Answers 3

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To plot $x=f(y)$ without having to mentally flip across the $y=x$ diagonal, you could plot $y = -f(x)$, then turn the calculator 90° counterclockwise. In your case, plot $y=-(x^2-6)$.

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    +1 But my calculator is on my iPad and when I turn it 90°, the calculator turns too! :-)2012-04-20
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    @DilipSarwate Then turn yourself or wait 18 hours ;-)2012-04-20
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    How to lock ipad screen :P :) http://www.howtogeek.com/howto/36330/how-to-lock-the-screen-orientation-on-your-ipad-with-ios-4.2/2012-04-21
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    @DilipSarwate Five years later, I've solved your problem: just multiply your iPad by $-i$, and then you'll have just a regular Pad that shouldn't change the display when you turn it. ;)2017-04-10
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You may :

  • graph $y=x^2-6$ and mentally reverse the $x$ and $y$ axis
  • graph $y=\sqrt{x+6}$ and $y=-\sqrt{x+6}$ obtaining the two required branches
  • use the parametric method $x=t^2-6,y=t$ proposed by The Chaz! (probably the best solution if it works...)
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    @Ekuurh: (-: !! sknahT2012-04-20
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    I can't understand why a modern graphing calculator wouldn't allow me to just enter the equation as is, but this solution works, and it's good mental exercise. Thank you for your reply.2012-04-20
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    If your brain doesn't have the reversion feature, you can turn it and then hold it up to a mirror :)2012-04-20
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    @ThomasAndrews: a mirror inclined at 45 degrees! :-)2012-04-20
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    Lol. Yeah. It's a minor nitpick, but still. :P2012-04-20
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    @RaymondManzoni (-: shvpvmou uowwo) h++3^d 3^v s^o^^!W2012-04-20
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    @dtldarek: Thanks for the effort! (Finally I was right not trying to 'Mirror' it! :-))2012-04-20
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GeoGebra allows entry directly in that form, eg

http://web.geogebra.org/?command=x=y^2-6