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I was just wondering, how do I plot a single variable inequality in Mathematica?

For example, we could use Wolfram Alpha for plotting an inequality like $x^3+4x+9 > 0$ and see something like this. How could we do the same thing in Mathematica?

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2 Answers 2

up vote 4 down vote accepted

How about this?

Plot[x^3+4x+9, {x,-2,2}, Filling->{1->{Axis, {White, LightBlue}}}]

Or, if you have two functions, and want where first curve is above the second, use

Plot[{x^3+4x+9,6x^2}, {x,-2,2}, Filling->{1->{{2}, {White, LightBlue}}}]

for example.

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Could you explain the plot?Especially the filling side,I haven't did anything using filling before. –  Quixotic Oct 16 '11 at 14:31
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Well, I suggest you read about the Filling option in the excellent help that accompanies Mathematica. Press F1, search for Filling. –  Per Alexandersson Oct 16 '11 at 16:03

There is also RegionPlot[]:

RegionPlot[x^3 + 4 x + 9 > y, {x, -2, 2}, {y, 0, 25}]

plots the part in blue.

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