Domain Analysis: Solving (x-6)² - 3 Function Boundaries

Quadratic Functions with Sign Analysis

Find the positive and negative domains of the function below:

y=(x6)23 y=\left(x-6\right)^2-3

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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=(x6)23 y=\left(x-6\right)^2-3

2

Step-by-step solution

To find the positive and negative domains of the function y=(x6)23 y = (x-6)^2 - 3 , follow these steps:

  • Step 1: Set y=0 y = 0 to find the roots of the equation. This gives us (x6)23=0(x-6)^2 - 3 = 0.
  • Step 2: Add 3 to both sides to simplify, resulting in (x6)2=3(x-6)^2 = 3.
  • Step 3: Take the square root of both sides. We have two solutions: x6=3 x - 6 = \sqrt{3} and x6=3 x - 6 = -\sqrt{3} .
  • Step 4: Solve for x x from each equation:
    • For x6=3 x - 6 = \sqrt{3} , x=6+3 x = 6 + \sqrt{3} .
    • For x6=3 x - 6 = -\sqrt{3} , x=63 x = 6 - \sqrt{3} .
  • Step 5: Determine the intervals:
    • Interval 1: x<63 x < 6 - \sqrt{3} , insert a test point to determine sign.
    • Interval 2: 63<x<6+3 6 - \sqrt{3} < x < 6 + \sqrt{3} , insert a test point to determine sign.
    • Interval 3: x>6+3 x > 6 + \sqrt{3} , insert a test point to determine sign.
  • Step 6: Based on the intervals:
    • For x<63 x < 6 - \sqrt{3} and x>6+3 x > 6 + \sqrt{3} , y>0 y > 0 .
    • For 63<x<6+3 6 - \sqrt{3} < x < 6 + \sqrt{3} , y<0 y < 0 .

The positive domains are: x<63 x < 6 - \sqrt{3} or x>6+3 x > 6 + \sqrt{3} .

The negative domain is: 63<x<6+3 6 - \sqrt{3} < x < 6 + \sqrt{3} .

The correct answer to the problem is:

x>6+3 x > 6+\sqrt{3} or x<0:x<63 x < 0 : x < 6-\sqrt{3}

x<0:63<x<6+3 x < 0 : 6-\sqrt{3} < x < 6+\sqrt{3}

3

Final Answer

x>6+3 x > 6+\sqrt{3} or x>0:x<63 x > 0 : x < 6-\sqrt{3}

x<0:63<x<6+3 x < 0 : 6-\sqrt{3} < x < 6+\sqrt{3}

Key Points to Remember

Essential concepts to master this topic
  • Domain Rule: Find where function equals zero to identify boundary points
  • Technique: Solve (x6)2=3 (x-6)^2 = 3 gives x=6±3 x = 6 \pm \sqrt{3}
  • Check: Test points in each interval: x=4 x = 4 gives positive value ✓

Common Mistakes

Avoid these frequent errors
  • Confusing positive/negative domains with function behavior
    Don't assume the function is positive when x > 0 and negative when x < 0 = wrong interpretation! The signs of x-values don't determine function signs. Always find where y = 0 first, then test intervals to determine where the function itself 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

What exactly are positive and negative domains?

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Positive domains are x-intervals where y > 0 (function output is positive), and negative domains are where y < 0 (function output is negative). It's about the function's sign, not the x-values' signs!

Why do I need to find the roots first?

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The roots (where y = 0) are the boundary points that separate positive and negative regions. These critical points tell you exactly where the function changes from positive to negative or vice versa.

How do I know which intervals are positive or negative?

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After finding the roots, test a point from each interval by substituting it into the original function. If the result is positive, that entire interval is positive; if negative, the interval is negative.

Why does this parabola have both positive and negative regions?

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Since y=(x6)23 y = (x-6)^2 - 3 is a parabola opening upward with vertex at (6, -3), it dips below the x-axis near x = 6, creating a negative region between the two roots.

What if I can't remember the square root steps?

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When you have (x6)2=3 (x-6)^2 = 3 , take the square root of both sides: x6=±3 x-6 = \pm\sqrt{3} . The ± gives you two solutions: add 6 to each to get your boundary points.

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