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What is the domain of the function \( g(x)=\sqrt{\frac{x-7}{x+9}} \) ? The domain is \( \square \). (Type your answer in interval notation. Simplify your answer. Use integers or fractions for any numbers in the expression.)

Ask by Ross Joseph. in the United States
Feb 21,2025

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The domain of the function \( g(x) = \sqrt{\frac{x-7}{x+9}} \) is \( (-\infty, -9) \cup [7, \infty) \).

Solution

To find the domain of g(x) = √((x - 7)/(x + 9)), we need the expression inside the square root to be nonnegative and the denominator to be nonzero. Step 1: Set the radicand nonnegative:   (x - 7)/(x + 9) ≥ 0 Step 2: Identify where the numerator or denominator equals zero:   Numerator: x - 7 = 0 ⟹ x = 7   Denominator: x + 9 = 0 ⟹ x = -9 (this value must be excluded) Step 3: Analyze the sign of (x - 7)/(x + 9) using a sign chart. - For x < -9:   Pick a test value (e.g., x = -10)   Numerator: -10 - 7 = -17 (negative)   Denominator: -10 + 9 = -1 (negative)   The fraction is positive (negative/negative > 0). - For -9 < x < 7:   Pick a test value (e.g., x = 0)   Numerator: 0 - 7 = -7 (negative)   Denominator: 0 + 9 = 9 (positive)   The fraction is negative (negative/positive < 0). - For x > 7:   Pick a test value (e.g., x = 8)   Numerator: 8 - 7 = 1 (positive)   Denominator: 8 + 9 = 17 (positive)   The fraction is positive. Step 4: Include endpoints where the inequality holds:   At x = 7, the numerator is 0, making the fraction 0, which is allowed.   x = -9 is excluded because it makes the denominator zero. Thus, the function is defined for x in (–∞, –9) (where the expression is positive) and for x in [7, ∞). The domain in interval notation is: (–∞, –9) ∪ [7, ∞).

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To determine the domain of the function \( g(x) = \sqrt{\frac{x-7}{x+9}} \), we need to ensure that the expression inside the square root is non-negative. This means \( \frac{x-7}{x+9} \geq 0 \). The critical points occur when \( x-7 = 0 \) or \( x+9 = 0 \), which gives us \( x = 7 \) and \( x = -9 \). Next, we analyze the intervals determined by these points: 1. **Interval \( (-\infty, -9) \)**: Choose \( x = -10 \): \( \frac{-10-7}{-10+9} = \frac{-17}{-1} = 17 \) (positive). 2. **Interval \( (-9, 7) \)**: Choose \( x = 0 \): \( \frac{0-7}{0+9} = \frac{-7}{9} \) (negative). 3. **Interval \( (7, \infty) \)**: Choose \( x = 8 \): \( \frac{8-7}{8+9} = \frac{1}{17} \) (positive). Thus, the function is non-negative in the intervals \( (-\infty, -9) \) and \( (7, \infty) \). The points \( x = -9 \) (undefined) and \( x = 7 \) (zero) must be treated accordingly: Consequently, the domain of \( g(x) \) is \( (-\infty, -9) \cup [7, \infty) \). So, the domain is \( \square (-\infty, -9) \cup [7, \infty) \).

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