Quadratic Expression with a Fixed Sign

Rarely Tested

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.

Question 1

The integer $$k$$, for which the inequality $$x^2 - 2(3k - 1)x + 8k^2 - 7 > 0$$ is valid for every $$x$$ in $$R$$ is:

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