Quadratic Expression with a Fixed Sign
## Formula
For:
$$ax^2+bx+c$$
to have a fixed positive sign:
$$a>0,\qquad D<0$$
For a fixed negative sign:
$$a<0,\qquad D<0$$
For a fixed non-negative sign:
$$a>0,\qquad D\le0$$
For a fixed non-positive sign:
$$a<0,\qquad D\le0$$
## Usage
- Used in inequalities and parameter problems where the expression must maintain a fixed sign.