Sign of quadratic expression on ℝ (Always positive parabola opens up and never meets x-axis; always)
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Always positive parabola opens up and never meets x-axis; always negative opens down and floats below
What each symbol means
| Symbol | What it stands for |
|---|---|
| D | b²−4ac |
| a | Leading coeff |
When to use this
Strict inequalities; non-strict allows touching (D=0) with care.