Determine X Values where the Quadratic Equation y = -x² is Positive

Quadratic Inequalities with Negative Coefficients

Given the function:

y=x2 y=-x^2

Determine for which values of x is f(x)>0 f\left(x\right) > 0 true

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Step-by-step written solution

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1

Understand the problem

Given the function:

y=x2 y=-x^2

Determine for which values of x is f(x)>0 f\left(x\right) > 0 true

2

Step-by-step solution

To solve the problem, we need to understand when the function y=x2 y = -x^2 is greater than 0.

1. **Analysis of the Function**: The given function is y=x2 y = -x^2 . Here, y y represents the output of the quadratic expression, where the coefficient of x2 x^2 is negative (1-1). This means that for every input x x , the output is the negative of x2 x^2 .

2. **Properties of the Square**: The expression x2 x^2 is always non-negative, i.e., x20 x^2 \geq 0 for all real numbers x x . This implies:

  • For x=0 x = 0 , x2=0 x^2 = 0 .
  • For any non-zero x x , x2>0 x^2 > 0 .

3. **Impact of the Negative Sign**: Since y=x2 y = -x^2 :

  • If x2=0 x^2 = 0 (which happens when x=0 x = 0 ), then y=0 y = 0 .
  • If x2>0 x^2 > 0 (which happens when x0 x \ne 0 ), then y<0 y < 0 .

4. **Conclusion on Positivity**: There are no values of x x for which y=x2 y = -x^2 is greater than 0, as y0 y \leq 0 for all real x x . Thus, the function is never positive.

Therefore, the solution to this problem is No x x .

3

Final Answer

x0 x\ne0

Key Points to Remember

Essential concepts to master this topic
  • Rule: Negative quadratics are always non-positive or zero
  • Technique: For y=x2 y = -x^2 , maximum value is 0 at x = 0
  • Check: Test any non-zero value: 22=4<0 -2^2 = -4 < 0

Common Mistakes

Avoid these frequent errors
  • Ignoring the negative sign's impact
    Don't think x2 -x^2 can be positive like x2 x^2 = wrong answers! The negative sign flips all values downward, making positive squares become negative. Always remember that x20 -x^2 ≤ 0 for all real x.

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

Why can't y=x2 y = -x^2 ever be positive?

+

Because x2 x^2 is always non-negative (zero or positive), so x2 -x^2 is always non-positive (zero or negative). The negative sign flips everything downward!

What's the maximum value of y=x2 y = -x^2 ?

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The maximum value is 0, which occurs when x=0 x = 0 . This is because 02=0 -0^2 = 0 , and for any other x-value, you get a negative result.

How is this different from y=x2 y = x^2 ?

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Great question! y=x2 y = x^2 opens upward with minimum value 0, while y=x2 y = -x^2 opens downward with maximum value 0. They're complete opposites!

So the answer is really 'No x'?

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Exactly! There are no x-values where x2>0 -x^2 > 0 . The function equals zero at x = 0 and is negative everywhere else. This is a valid mathematical result!

What if the problem asked for f(x)0 f(x) ≥ 0 instead?

+

Then the answer would be x=0 x = 0 only! The symbol includes when the function equals zero, which happens exactly when x = 0.

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