Equations - Quadratic Inequation

Quadratic Inequation

General Form:

\[ ax^2 + bx + c > 0 \quad \text{where } a \neq 0 \]

Terminology:

  • \( a \): Coefficient of \( x^2 \), determines the direction of the parabola (opens up if \( a > 0 \), down if \( a < 0 \)).
  • \( b \): Coefficient of \( x \).
  • \( c \): Constant term.
  • Discriminant (\( \Delta \)): \( b^2 - 4ac \), determines the number and type of roots.
  • Roots: Values of \( x \) where \( ax^2 + bx + c = 0 \), denoted \( x_1 \) and \( x_2 \).

Solution Cases:

Case 1: If \( a > 0 \)

  • \( b^2 - 4ac < 0 \): The quadratic expression is always positive ⇒ inequality holds for all real \( x \).
  • \( b^2 - 4ac = 0 \): Expression is positive for all \( x \ne -\frac{b}{2a} \).
  • \( b^2 - 4ac > 0 \): Expression is positive outside the interval between roots ⇒ \( x < x_1 \) or \( x > x_2 \).

Case 2: If \( a < 0 \)

  • \( b^2 - 4ac \leq 0 \): Expression never positive ⇒ no real solution.
  • \( b^2 - 4ac > 0 \): Expression is positive between the roots ⇒ \( x_1 < x < x_2 \).

Quadratic Formula (for finding roots):

\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]

Applications:

  • Physics: Used in projectile motion and kinematic equations.
  • Engineering: In designing curves like bridges, arches, and lenses.
  • Economics: For analyzing profit, loss, and cost curves.
  • Computer Science: In algorithm optimization and graphics rendering.
  • Mathematics: Solving inequalities and graphing parabolas.
Quadratic Inequation
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