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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$ – The Chaz 2.0 Apr 20 '12 at 20:57
I use the app Desmos, It's free so I would recommend it @Subtle Array – Ahmed S. Attaalla Jan 3 at 5:53
up vote 9 down vote accepted

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: Fine composition! – Raymond Manzoni Apr 20 '12 at 21:19
+1 But my calculator is on my iPad and when I turn it 90°, the calculator turns too! :-) – Dilip Sarwate Apr 20 '12 at 21:33
@DilipSarwate Then turn yourself or wait 18 hours ;-) – dtldarek Apr 20 '12 at 21:35
How to lock ipad screen :P :)… – Gordon Gustafson Apr 21 '12 at 1:58

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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+1'd for mental reversion :) – Ekuurh Apr 20 '12 at 21:00
@Ekuurh: (-: !! sknahT – Raymond Manzoni Apr 20 '12 at 21:02
If your brain doesn't have the reversion feature, you can turn it and then hold it up to a mirror :) – Thomas Andrews Apr 20 '12 at 21:06
@ThomasAndrews: a mirror inclined at 45 degrees! :-) – Raymond Manzoni Apr 20 '12 at 21:08
Lol. Yeah. It's a minor nitpick, but still. :P – Subtle Array Apr 20 '12 at 21:09

GeoGebra allows entry directly in that form, eg^2-6

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