Question

True or False If the discriminant \(b^{2}-4 a c=0,\) the graph of \(f(x)=a x^{2}+b x+c, a \neq 0,\) touches the \(x\) -axis at its vertex.

Short answer

True

Step-by-step solution

- Understand the Discriminant

The discriminant of a quadratic equation is given by the expression \(b^2 - 4ac\). This value helps determine the nature of the roots for the quadratic equation \(ax^2 + bx + c = 0\).

- Interpret the Discriminant Value

If \(b^2 - 4ac = 0\), it means the quadratic equation has exactly one real root. This root occurs where the parabola defined by \(f(x) = ax^2 + bx + c\) touches the x-axis.

- Relationship Between Vertex and Roots

When \(b^2 - 4ac = 0\), the single root (or repeated root) of the quadratic function is at the vertex. Thus, the graph of the quadratic function touches the x-axis precisely at its vertex.

- Conclusion

Given that \(b^2 - 4ac = 0\) means the graph touches the x-axis at exactly one point and that point is the vertex, the statement is TRUE. \(f(x) = ax^2 + bx + c\) touches the x-axis at its vertex.

Key concepts

discriminant

The discriminant is a key concept in quadratic equations. Given by the expression \( b^2 - 4ac \), it helps us understand the nature of the roots of a quadratic equation. The quadratic equation in standard form is \( ax^2 + bx + c = 0 \). The value of the discriminant fundamentally tells us whether the roots are real or complex, and if real, whether they are distinct or identical.

Here’s a breakdown of what the discriminant tells us:

• If \( b^2 - 4ac > 0 \), there are two distinct real roots.
• If \( b^2 - 4ac = 0 \), there is exactly one real root (also called a double root).
• If \( b^2 - 4ac < 0 \), the roots are complex (not real).

Understanding the discriminant helps in sketching the graph of a quadratic function and predicting where it intersects the x-axis. For instance, when \( b^2 - 4ac = 0 \), the parabola touches the x-axis at exactly one point, indicating a perfect square trinomial equation.

quadratic equations

Quadratic equations are polynomial equations of degree 2. They have the general form \( ax^2 + bx + c = 0 \). These equations graphically represent parabolas, which are U-shaped curves.

Key aspects of quadratic equations include:

• The coefficient \( a \) determines the direction of the parabola. If \( a > 0 \), the parabola opens upwards; if \( a < 0 \), it opens downwards.
• The vertex of the parabola is the peak or trough, depending on the direction it opens. It's a significant point that represents either the maximum or minimum value of the quadratic function.
• The roots (solutions) of the quadratic equation where \( ax^2 + bx + c = 0 \) are the points where the parabola intersects the x-axis.

Quadratic equations are commonly solved using various methods, such as factoring, completing the square, or using the quadratic formula. The discriminant within the quadratic formula is crucial because it guides us in understanding the types of solutions to expect.

vertex

The vertex of a quadratic function \( f(x) = ax^2 + bx + c \) is a central point of the graph and is either the highest or lowest point, depending on the direction of the parabola.

The vertex can be found using the formula:

• Vertex \( x \text{-coordinate}: \ x = -\frac{b}{2a} \)

Once you have the \( x \text{-coordinate} \), you can find the corresponding \( y \text{-coordinate} \) by plugging this \( x \) value back into the original equation.

When the discriminant \( b^2 - 4ac = 0 \), the only root of the quadratic equation occurs at the vertex. In other words:

• If the discriminant is zero, the parabola touches the x-axis exactly once at its vertex, making it a point of tangency.

This means the vertex represents the point where the quadratic function changes direction. In summary, the vertex is a crucial element in understanding and interpreting the graphical plot of a quadratic equation.