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 intersects the X-axis at points A and B.

The vertex of the parabola is marked at point C.

Find all values of \( x \) where \( f\left(x\right) > 0 \).

AAABBBCCCX

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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