Empty ContourPlots when using symbol with assigned equation

Questions
1

Why don’t the first two contour plots show the equation?

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2

Jay,

ContourPlot has the attribute HoldAll:

Attributes[ContourPlot]
(*  Out:   {HoldAll,Protected,ReadProtected}   *)

So, you need Evaluate:

eq1 = x^2 - y (x - 1) == 0;
ContourPlot[Evaluate@eq1, {x, -5, 5}, {y, -5, 5}]
3

Thanks, Henrik Schachner. That works. I’m reading about Evaluate now.