Parabola Properties: Analyzing Negative Values with Downward-Facing Vertex Below X-axis

Quadratic Functions with Vertex Position Analysis

If a parabola is bending downwards and its vertex is below the x-axis, then it is always negative.

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

If a parabola is bending downwards and its vertex is below the x-axis, then it is always negative.

2

Step-by-step solution

The problem concerns a downward-opening parabola with a vertex below the x-axis. Let's elaborate on these terms to determine if the given statement is correct:

  • Step 1: Identify Quadratic Form
    We consider a quadratic function f(x)=ax2+bx+c f(x) = ax^2 + bx + c with a<0 a < 0 since it opens downwards.
  • Step 2: Understand the Vertex's Position
    The vertex form of the quadratic is f(x)=a(xh)2+k f(x) = a(x - h)^2 + k . Given that the vertex is below the x-axis, the condition k<0 k < 0 holds. The vertex at coordinate (h,k)(h, k) is the maximum point of the parabola.
  • Step 3: Evaluate the Parabola's Sign
    Since k<0 k < 0 , the vertex (h,k) (h, k) is the highest point of the parabola lying below the x-axis. Consequently, all other points on the parabola satisfy f(x)k<0 f(x) \leq k < 0 .

Therefore, the entire quadratic function is negative for all values of x x due to the vertex being the maximum and its y-coordinate being negative. Thus, the statement that such a parabola is always negative is indeed "correct".

Thus, the correct choice is: Correct \text{Correct} .

3

Final Answer

Correct

Key Points to Remember

Essential concepts to master this topic
  • Rule: Downward parabola vertex is the maximum point on graph
  • Technique: If vertex at (h,k) with k < 0, then f(x) ≤ k < 0
  • Check: Maximum value below x-axis means all function values negative ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting vertex is the maximum for downward parabolas
    Don't assume the parabola crosses the x-axis somewhere = incorrect analysis! When the vertex is below the x-axis and it's the highest point, no part of the parabola can reach above to cross the x-axis. Always remember the vertex represents the maximum for downward-opening parabolas.

Practice Quiz

Test your knowledge with interactive questions

The graph of the function below does not intersect the \( x \)-axis.

The parabola's vertex is marked A.

Find all values of \( x \) where
\( f\left(x\right) > 0 \).

AAAX

FAQ

Everything you need to know about this question

How do I know if a parabola opens downward?

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Look at the coefficient of x2 x^2 ! If a < 0 in f(x)=ax2+bx+c f(x) = ax^2 + bx + c , the parabola opens downward like an upside-down U.

What if the vertex is exactly on the x-axis?

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If the vertex is on the x-axis (k = 0), then the parabola touches the x-axis at exactly one point. The function equals zero at that point but is negative everywhere else.

Could a downward parabola ever have positive values?

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Only if its vertex is above the x-axis! When the vertex (maximum point) is above the x-axis, part of the parabola will be positive before it crosses down to negative values.

How do I find where the vertex is located?

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Use the vertex formula: h=b2a h = -\frac{b}{2a} for the x-coordinate, then substitute to find k=f(h) k = f(h) for the y-coordinate.

Why is this important to understand?

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Sign analysis helps you understand function behavior! Knowing when a quadratic is always positive, always negative, or changes sign is crucial for solving inequalities and real-world applications.

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