Exploring the Domain of the Function: √(4x² - 8)/5

Domain of Functions with Square Root Expressions

Look at the following function:

4x285 \frac{\sqrt{4x^2-8}}{5}

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
00:08 First, let's see if the function can have a domain of definition. And if it can, what would that be?
00:14 Remember, the denominator can't be zero, so we'll check that first.
00:19 Since there are no restrictions for the denominator, let's examine the numerator next.
00:25 The square root needs to be a positive number.
00:29 To solve, we'll set this part equal to zero and find the values that work.
00:33 Let's focus now on isolating the variable X.
00:40 Remember, finding a square root gives us two solutions: one positive, one negative.
00:46 Let's sketch it out to clearly see the domain of definition.
00:54 Between these solutions, any value of X would result in a negative root.
01:01 And that's how we solve this problem, finding the function's domain.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Look at the following function:

4x285 \frac{\sqrt{4x^2-8}}{5}

What is the domain of the function?

2

Step-by-step solution

To determine the domain of the function 4x285 \frac{\sqrt{4x^2 - 8}}{5} , we must ensure the expression under the square root is non-negative. This condition will make the function well-defined over the real numbers.

Steps to solve for the domain:

  • Step 1: Set the expression inside the square root greater or equal to zero: 4x280 4x^2 - 8 \geq 0 .
  • Step 2: Solve the inequality.

To solve the inequality 4x280 4x^2 - 8 \geq 0 :

Step 3: Add 8 to both sides:

4x28 4x^2 \geq 8

Step 4: Divide each term by 4 to simplify:

x22 x^2 \geq 2

Step 5: Solve for x x . When an inequality involves a square, interpret it as involving two cases. Thus, x2 x \geq \sqrt{2} OR x2 x \leq -\sqrt{2} .

This inequality describes the values of x x for which the function is defined. These constitute the domain of the function. Therefore, the domain is x2 x \geq \sqrt{2} or x2 x \leq -\sqrt{2} .

The correct answer choice is:

x2,x2 x\ge\sqrt{2},x\le-\sqrt{2}

3

Final Answer

x2,x2 x\ge\sqrt{2},x\le-\sqrt{2}

Key Points to Remember

Essential concepts to master this topic
  • Domain Rule: Expression under square root must be non-negative
  • Technique: Set 4x280 4x^2 - 8 \geq 0 , solve to get x22 x^2 \geq 2
  • Check: Test x=2 x = \sqrt{2} : 4(2)8=00 4(2) - 8 = 0 \geq 0

Common Mistakes

Avoid these frequent errors
  • Taking square root of both sides incorrectly
    Don't solve x22 x^2 \geq 2 as just x2 x \geq \sqrt{2} = missing negative values! This ignores that x2 x^2 makes both positive and negative values positive. Always remember x22 x^2 \geq 2 means x2 x \geq \sqrt{2} OR x2 x \leq -\sqrt{2} .

Practice Quiz

Test your knowledge with interactive questions

\( \frac{6}{x+5}=1 \)

What is the field of application of the equation?

FAQ

Everything you need to know about this question

Why can't the expression under the square root be negative?

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In real numbers, you cannot take the square root of a negative number. If 4x28<0 4x^2 - 8 < 0 , then 4x28 \sqrt{4x^2 - 8} would be undefined!

How do I solve x22 x^2 \geq 2 ?

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Think about it this way: what values of x make x2 x^2 at least 2? Both large positive and large negative values work! So x2 x \geq \sqrt{2} or x2 x \leq -\sqrt{2} .

What does x2,x2 x \geq \sqrt{2}, x \leq -\sqrt{2} mean?

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This means x can be either greater than or equal to 2 \sqrt{2} or less than or equal to 2 -\sqrt{2} . It's two separate regions on the number line!

Why isn't the domain all real numbers?

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Because when 2<x<2 -\sqrt{2} < x < \sqrt{2} , we get x2<2 x^2 < 2 , making 4x28<0 4x^2 - 8 < 0 . The square root of a negative number is undefined in real numbers.

How do I check my domain answer?

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Test boundary values: Try x=2 x = \sqrt{2} and x=2 x = -\sqrt{2} . Both should make 4x28=0 4x^2 - 8 = 0 . Also test a value between them like x=0 x = 0 - this should be undefined!

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