Put it in the form: ax2 + bx + c =0
The disciminant: b2 - 4ac
If...
b2 - 4ac > 0 it has 2 distinct real roots / crosses the x-axis twice
b2 - 4ac = 0 it has 1 real root (or two repeated roots) / crosses the x-axis once
b2 - 4ac < 0 it has no real roots / never crosses the x-axis
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