Find the Domain of y=-(x-12)²+2: Analyzing Input Values

Quadratic Functions with Sign Analysis

Find the positive and negative domains of the function below:

y=(x12)2+2 y=-\left(x-12\right)^2+2

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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=(x12)2+2 y=-\left(x-12\right)^2+2

2

Step-by-step solution

To solve this problem, follow these steps:

  • Step 1: Find the roots of the function. Set y=0=(x12)2+2 y = 0 = -\left(x-12\right)^2 + 2 .

  • Step 2: Rearrange and solve for x x : (x12)2+2=0(x12)2=2 \begin{aligned} -\left(x-12\right)^2 + 2 &= 0 \\ \left(x-12\right)^2 &= 2 \end{aligned} Solving gives x12=±2 x - 12 = \pm \sqrt{2} , resulting in roots x=12+2 x = 12 + \sqrt{2} and x=122 x = 12 - \sqrt{2} .

  • Step 3: Determine the intervals: x<122122<x<12+2x>12+2 \begin{aligned} x < 12 - \sqrt{2} \\ 12 - \sqrt{2} < x < 12 + \sqrt{2} \\ x > 12 + \sqrt{2} \end{aligned} Step 4: Test each interval to check the sign of y y : \begin{itemize}

  • For x<122 x < 12 - \sqrt{2} and x>12+2 x > 12 + \sqrt{2} , (x12)2 (x-12)^2 becomes larger than 2, so y=[(x12)2]+2 y= -[(x-12)^2] + 2 is negative.

  • For 122<x<12+2 12 - \sqrt{2} < x < 12 + \sqrt{2} , (x12)2 (x-12)^2 is less than 2, so y=[(x12)2]+2 y = -[(x-12)^2] + 2 is positive.

Thus, the function is negative for x>12+2 x > 12 + \sqrt{2} or x<122 x < 12 - \sqrt{2} , and positive for 122<x<12+2 12 - \sqrt{2} < x < 12 + \sqrt{2} .

Therefore, the positive and negative domains of the function are:

x>12+2 x > 12+\sqrt{2} or x<0:x<122 x < 0 : x < 12-\sqrt{2}

x>0:122<x<12+2 x > 0 : 12-\sqrt{2} < x < 12+\sqrt{2}

3

Final Answer

x>12+2 x > 12+\sqrt{2} or x<0:x<122 x < 0 : x < 12-\sqrt{2}

x>0:122<x<12+2 x > 0 : 12-\sqrt{2} < x < 12+\sqrt{2}

Key Points to Remember

Essential concepts to master this topic
  • Zeros First: Set function equal to zero and solve completely
  • Technique: Use (x12)2=2 (x-12)^2 = 2 to get x=12±2 x = 12 \pm \sqrt{2}
  • Check: Test values in each interval to verify positive/negative signs ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to analyze signs between intervals
    Don't just find the zeros and stop = incomplete answer! Finding x=12±2 x = 12 \pm \sqrt{2} only gives boundary points. Always test values in each interval to determine where the function is positive or negative.

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 do I need to find where the function equals zero first?

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The zeros divide the number line into intervals where the function doesn't change sign. Think of it like crossing a bridge - the function can only change from positive to negative (or vice versa) at these crossing points!

How do I know which intervals are positive or negative?

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Pick any test value in each interval and substitute it into the original function. If you get a positive result, that entire interval is positive. If negative, the whole interval is negative.

What does the negative sign in front of the function do?

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The negative sign flips the parabola upside down. Since (x12)2 (x-12)^2 is always positive, adding the negative makes it an inverted parabola that opens downward.

Why is the answer split into positive and negative domains?

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The question asks for separate domains where the function is positive vs negative. You need to identify all x-values where y > 0 (positive domain) and all x-values where y < 0 (negative domain).

How do I handle the square root in my answer?

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Keep 2 \sqrt{2} in exact form unless told to use decimals. The exact boundaries are x=122 x = 12 - \sqrt{2} and x=12+2 x = 12 + \sqrt{2} , which create three distinct intervals.

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