Finding Negative Values of a Parabolic Function with Vertex on X-axis

Parabolas with Vertex on X-axis

The graph of the function below intersects the x x -axis at point A (the vertex of the parabola).

Find all values of x x wheref(x)<0 f\left(x\right) < 0 .

AAAX

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Step-by-step written solution

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1

Understand the problem

The graph of the function below intersects the x x -axis at point A (the vertex of the parabola).

Find all values of x x wheref(x)<0 f\left(x\right) < 0 .

AAAX

2

Step-by-step solution

To solve this problem, we need to determine when f(x) f(x) is negative by analyzing the graph provided.

The graph shows a quadratic function shaped as a parabola. Importantly, the parabola intersects the x-axis precisely at point A, which is its vertex. From this, we can deduce two possible scenarios:

1. If the parabola opens upwards (convex), the vertex represents the minimum point. Thus, the y-value at the vertex is greater than any other point on the function, implying there is no region where f(x)<0 f(x) < 0 since the lowest point is zero.

2. If it were to open downwards, point A would be the maximum, and f(x) f(x) could be negative elsewhere, but this contradicts the given information that point A is a vertex on the x-axis, suggesting the opening is upwards.

Since the graph passes through the x-axis only at vertex A and that is the minimum point, the parabola opens upwards. Therefore, the function f(x) f(x) never takes negative values as it only touches the x-axis without crossing it.

Thus, the conclusion is that there are no values of x x for which f(x)<0 f(x) < 0 .

Hence, the function has no negative domain.

3

Final Answer

The function has no negative domain.

Key Points to Remember

Essential concepts to master this topic
  • Vertex Position: When vertex touches x-axis, parabola opens upward
  • Technique: Check if function crosses or just touches axis
  • Check: Upward parabola touching x-axis never goes below zero ✓

Common Mistakes

Avoid these frequent errors
  • Assuming parabola must have negative values somewhere
    Don't think all parabolas cross the x-axis = wrong negative domain! When the vertex is on the x-axis and opens upward, the function only touches zero but never goes negative. Always check if the parabola opens up or down from its vertex.

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 upward or downward?

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Look at the shape direction! If it looks like a 'U', it opens upward. If it looks like an upside-down 'U', it opens downward. The graph shows a U-shape.

What does it mean when the vertex is on the x-axis?

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When the vertex touches the x-axis, that's the turning point of the parabola. For upward-opening parabolas, this is the lowest point, so the function never goes below zero.

Can a parabola touch the x-axis without crossing it?

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Yes! When a parabola has its vertex on the x-axis, it touches the axis at exactly one point but doesn't cross over to the other side.

Why does this parabola have no negative values?

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Since the parabola opens upward and its lowest point (vertex) is at zero on the x-axis, all other points must be above the x-axis, making f(x)0 f(x) \geq 0 everywhere.

What if the parabola opened downward instead?

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If it opened downward with vertex on the x-axis, then the vertex would be the highest point, and the function would be negative everywhere else except at the vertex.

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