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Bunuel
­The domain of the function \(f(x) = \frac{\sqrt{|x| - 2}}{\sqrt{\sqrt{x + 9}- \sqrt{3 - x}}}\) is the set of real numbers x such that:

A. \(-3 < x ≤ -2\) or \(2 ≤ x < 3\)

B. \(-3 < x ≤ -2\) or \(2 ≤ x ≤ 3\)

C. \(-3 ≤ x ≤ -2\) or \(2 ≤ x ≤ 3\)

D. \(-9 ≤ x < -3\) or \(-3 < x ≤ -2\) or \(2 ≤ x ≤ 3\)
 
E. \(-9 ≤ x ≤ -2\) or \(2 ≤ x ≤ 3\)­


 


This question was provided by GMAT Club
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­

In this function
Square root can't be negative
Denomination can't be zero
Root of 3-x can't be greater than root of x+9

If you plot, +2,-2,-9,-3,3 on a number line & check the function

Range will be satisfied by option B

IMO B

Posted from my mobile device
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Bunuel why aren't we considering -9?
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Bunuel
­The domain of the function \(f(x) = \frac{\sqrt{|x| - 2}}{\sqrt{\sqrt{x + 9}- \sqrt{3 - x}}}\) is the set of real numbers x such that:

A. \(-3 < x ≤ -2\) or \(2 ≤ x < 3\)

B. \(-3 < x ≤ -2\) or \(2 ≤ x ≤ 3\)

C. \(-3 ≤ x ≤ -2\) or \(2 ≤ x ≤ 3\)

D. \(-9 ≤ x < -3\) or \(-3 < x ≤ -2\) or \(2 ≤ x ≤ 3\)

E. \(-9 ≤ x ≤ -2\) or \(2 ≤ x ≤ 3\)
­

GMAT Club Official Explanation:



Given that the expression contains a fraction and square roots, the domain of the function will be defined when the square roots are greater than or equal to 0 (since even roots are not defined for negative numbers) and the denominator of the fraction is not equal to 0 (since division by 0 is not allowed). Thus, the following conditions must be satisfied simultaneously:


1. The expression inside the square root in the numerator, |x| - 2, must be non-negative:

|x| - 2 ≥ 0
|x| ≥ 2
This means x ≤ -2 or x ≥ 2.

--------------------------(-2)--------(2)-------

2. The individual expressions inside the square roots in the denominator, x + 9, and 3 - x must be non-negative:

x + 9 ≥ 0 and 3 - x ≥ 0
x ≥ -9 and x ≤ 3
This means -9 ≤ x ≤ 3.

--(-9)-------------------------------------(3)--

3. The whole expression inside the square roots in the denominator must be positive:

\(\sqrt{x + 9} - \sqrt{3 - x} > 0\)
\(\sqrt{x + 9} > \sqrt{3 - x}\)
\(x + 9 > 3 - x\)
\(2x > -6\)
\(x > -3\)

-------------------(-3)---------------------------

The overlap of these ranges is \(-3 < x ≤ -2\) and \(2 ≤ x ≤ 3\).

--(-9)------------(-3)--(-2)--------(2)--(3)--

Answer: B.­
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Bunuel why aren't we considering -9?
Bunuel
Bunuel
­The domain of the function \(f(x) = \frac{\sqrt{|x| - 2}}{\sqrt{\sqrt{x + 9}- \sqrt{3 - x}}}\) is the set of real numbers x such that:

A. \(-3 < x ≤ -2\) or \(2 ≤ x < 3\)

B. \(-3 < x ≤ -2\) or \(2 ≤ x ≤ 3\)

C. \(-3 ≤ x ≤ -2\) or \(2 ≤ x ≤ 3\)

D. \(-9 ≤ x < -3\) or \(-3 < x ≤ -2\) or \(2 ≤ x ≤ 3\)

E. \(-9 ≤ x ≤ -2\) or \(2 ≤ x ≤ 3\)
­

GMAT Club Official Explanation:



Given that the expression contains a fraction and square roots, the domain of the function will be defined when the square roots are greater than or equal to 0 (since even roots are not defined for negative numbers) and the denominator of the fraction is not equal to 0 (since division by 0 is not allowed). Thus, the following conditions must be satisfied simultaneously:


1. The expression inside the square root in the numerator, |x| - 2, must be non-negative:

|x| - 2 ≥ 0
|x| ≥ 2
This means x ≤ -2 or x ≥ 2.

--------------------------(-2)--------(2)-------

2. The individual expressions inside the square roots in the denominator, x + 9, and 3 - x must be non-negative:

x + 9 ≥ 0 and 3 - x ≥ 0
x ≥ -9 and x ≤ 3
This means -9 ≤ x ≤ 3.

--(-9)-------------------------------------(3)--

3. The whole expression inside the square roots in the denominator must be positive:

\(\sqrt{x + 9} - \sqrt{3 - x} > 0\)
\(\sqrt{x + 9} > \sqrt{3 - x}\)
\(x + 9 > 3 - x\)
\(2x > -6\)
\(x > -3\)

-------------------(-3)---------------------------

The overlap of these ranges is \(-3 < x ≤ -2\) and \(2 ≤ x ≤ 3\).

--(-9)------------(-3)--(-2)--------(2)--(3)--

Answer: B.­

We don’t include -9 (or any x ≤ -3) because √(x + 9) - √(3 - x) becomes zero or negative there, and since it’s in the denominator AND under a square root, the expression is undefined.
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