Domain Analysis: Finding Valid Inputs for y=-(x-2 6/19)²-2

Quadratic Functions with Vertex Form Analysis

Find the positive and negative domains of the function below:

y=(x2619)22 y=-\left(x-2\frac{6}{19}\right)^2-2

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Find the positive and negative domains of the function below:

y=(x2619)22 y=-\left(x-2\frac{6}{19}\right)^2-2

2

Step-by-step solution

To solve this problem, we must analyze the quadratic function y=(x2619)22 y = -\left(x - 2\frac{6}{19}\right)^2 - 2 to determine its positive and negative domains.

  • Step 1: Identify the vertex and direction
    The given function is in the form y=a(xh)2+k y = a(x - h)^2 + k , where a=1 a = -1 , h=2619 h = 2\frac{6}{19} , and k=2 k = -2 . The vertex of the parabola is at (2619,2) (2\frac{6}{19}, -2) .
  • Step 2: Analyze the direction of the parabola
    Since a=1 a = -1 (negative), the parabola opens downward. This indicates the vertex is at the maximum point of the parabola.
  • Step 3: Determine the function's values
    Since the maximum value of the function (at the vertex) is y=2 y = -2 , and the parabola opens downward, the function cannot be positive anywhere. It is always less than or equal to 2-2, so it's negative for all x x .
  • Step 4: Establish the positive and negative domains
    Since the function is always negative, there are no positive domains. Therefore, the negative domain for the function is all real numbers x \>.

Therefore, the positive and negative domains are:

\( x > 0 : none

x<0: x < 0 : all x x

3

Final Answer

x>0: x > 0 : none

x<0: x < 0 : all x x

Key Points to Remember

Essential concepts to master this topic
  • Vertex Form: y=a(xh)2+k y = a(x - h)^2 + k reveals vertex at (h, k)
  • Sign Analysis: When a = -1, parabola opens downward with maximum at vertex
  • Domain Check: Compare function's maximum value -2 with zero to determine signs ✓

Common Mistakes

Avoid these frequent errors
  • Confusing positive/negative domains with function values
    Don't assume positive x means positive y values = wrong domain classification! The question asks where the function is positive or negative, not where x is positive or negative. Always analyze the function's output values, not input signs.

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

What exactly are positive and negative domains?

+

Positive domain: x-values where y > 0 (function output is positive)
Negative domain: x-values where y < 0 (function output is negative)

This is about the function's values, not whether x itself is positive or negative!

How do I know if a parabola opens up or down?

+

Look at the coefficient a in y=a(xh)2+k y = a(x - h)^2 + k :

  • If a > 0: opens upward (smile shape)
  • If a < 0: opens downward (frown shape)

Here, a = -1, so it opens downward.

Why is the maximum value -2 and not something positive?

+

The vertex is at (2619,2) (2\frac{6}{19}, -2) , which means the highest point the parabola reaches is y = -2. Since the parabola opens downward, all other points are even lower (more negative).

Could this function ever be positive anywhere?

+

No! Since the maximum value is -2 and the parabola opens downward, every point on the graph has y ≤ -2. The function is always negative for all real numbers x.

What if the vertex was above the x-axis instead?

+

If the vertex had a positive y-value (like y = 3), then the function would be positive near the vertex and negative farther away, giving us both positive and negative domains to identify.

🌟 Unlock Your Math Potential

Get unlimited access to all 18 The Quadratic Function questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime

More Questions

Click on any question to see the complete solution with step-by-step explanations