Signe d'un trinôme du second degré (Sign of a Quadratic Trinomial)
This page presents a comprehensive theorem on the sign of a quadratic trinomial, which is crucial for understanding the behavior of quadratic functions. The theorem is divided into three main cases, each corresponding to different values of the discriminant (Δ).
Definition: A trinôme du second degré is a polynomial of degree 2, typically written in the form ax² + bx + c, where a ≠ 0.
The theorem states:
- If Δ < 0, the trinomial has the same sign as 'a' for all real values of x.
- If Δ = 0, the trinomial has the same sign as 'a' for all real values of x, except at x₀, where it equals zero.
- If Δ > 0, the trinomial has the same sign as 'a' outside the roots, the opposite sign between the roots, and equals zero at x₁ and x₂.
Highlight: The sign of the coefficient 'a' plays a crucial role in determining the overall behavior of the quadratic trinomial.
The page also includes visual representations of these cases, showing the graphs of the quadratic functions for each scenario. These graphs illustrate how the parabola intersects the x-axis (or doesn't) based on the value of Δ.
Example: For Δ < 0, the graph doesn't cross the x-axis, maintaining the same sign throughout. For Δ = 0, the graph touches the x-axis at one point, while for Δ > 0, it crosses the x-axis at two points.
Additionally, the page provides factorization forms for each case:
- For Δ < 0: a(x - α)² + β
- For Δ = 0: a(x - x₀)²
- For Δ > 0: a(x - x₁)(x - x₂)
Vocabulary: The forme canonique (canonical form) of a quadratic trinomial is a(x - α)² + β, which is particularly useful for understanding the vertex and symmetry of the parabola.
Understanding these concepts is essential for solving problems involving trinôme du second degré exercices and for mastering topics like factorisation d'un trinome du second degré.