Determining the Domain of 4/√(x+8): A Function Analysis

Domain Analysis with Square Root Denominators

Look at the following function:

4x+8 \frac{4}{\sqrt{x+8}}

What is the domain of the function?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Does the function have a domain? And if so, what is it?
00:03 The root must be for a positive number greater than 0
00:10 Let's isolate X
00:13 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Look at the following function:

4x+8 \frac{4}{\sqrt{x+8}}

What is the domain of the function?

2

Step-by-step solution

To solve this problem, we need to determine the domain of the function given by:

f(x)=4x+8 f(x) = \frac{4}{\sqrt{x+8}}

We must ensure that the function is defined for all x x . This involves considering the conditions under which the square root is valid and the denominator is non-zero.

Step 1: Analyze the square root expression x+8 \sqrt{x+8} . The expression inside the square root must be non-negative:

x+80 x + 8 \ge 0

Step 2: Solve the inequality:

  • Subtract 8 from both sides: x8 x \ge -8

Step 3: Consider the division by zero issue. The denominator x+8\sqrt{x+8} must be strictly greater than zero to avoid division by zero. Thus, we adjust the inequality to:

x+8>0 x + 8 > 0

Step 4: Solve the second inequality:

  • Subtract 8 from both sides: x>8 x > -8

Thus, the domain of the function is all x x such that x>8 x > -8 .

Review of the answer choices shows that the correct choice, consistent with our findings, is:

x>8 x > -8

Therefore, the domain of the function is x>8 x > -8 .

3

Final Answer

x>8 x > -8

Key Points to Remember

Essential concepts to master this topic
  • Square Root Rule: Expression under radical must be non-negative
  • Technique: For x+8 \sqrt{x+8} , solve x + 8 > 0 to get x > -8
  • Check: Test x = -7: 7+8=1=1 \sqrt{-7+8} = \sqrt{1} = 1

Common Mistakes

Avoid these frequent errors
  • Using ≥ instead of > for the domain
    Don't write x ≥ -8 when there's division by zero at x = -8! At x = -8, √(x+8) = 0 making the fraction undefined. Always use x > -8 to exclude the point where the denominator equals zero.

Practice Quiz

Test your knowledge with interactive questions

\( 22(\frac{2}{x}-1)=30 \)

What is the domain of the equation above?

FAQ

Everything you need to know about this question

Why can't x equal -8 if the square root is defined there?

+

While 8+8=0=0 \sqrt{-8+8} = \sqrt{0} = 0 is mathematically valid, we have division by zero in the denominator! Since 40 \frac{4}{0} is undefined, x = -8 must be excluded from the domain.

How do I remember when to use > versus ≥?

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Ask yourself: "Is there division involved?" If the square root is in the denominator, use > to avoid division by zero. If it's just in the numerator or by itself, use .

What if I had √(x+8) + 3 instead?

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Without division, you'd only need x+80 x + 8 \geq 0 , so x ≥ -8. The key difference is whether the square root appears in a denominator!

How can I check if x = -7 works?

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Substitute: f(7)=47+8=41=41=4 f(-7) = \frac{4}{\sqrt{-7+8}} = \frac{4}{\sqrt{1}} = \frac{4}{1} = 4 . Since we get a real number, x = -7 is in the domain!

What does the domain (-8, ∞) mean in interval notation?

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The parenthesis around -8 means -8 is not included (open interval). The domain includes all real numbers greater than -8, extending infinitely to the right.

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