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The domain of f(x)=(x)/(16-x^(2))+log(2)...

The domain of `f(x)=(x)/(16-x^(2))+log_(2)(x^(3)-2x)` is

A

`(-sqrt2,0)uu(sqrt2, oo)`

B

`(-sqrt2, 0)uu(sqrt2, 4)`

C

`(-sqrt2, 0)uu(4, 00)`

D

`(-sqrt2,0)uu(sqrt2, 4)uu(4,oo)`

Text Solution

AI Generated Solution

The correct Answer is:
To find the domain of the function \( f(x) = \frac{x}{16 - x^2} + \log_2(x^3 - 2x) \), we need to consider the restrictions imposed by both the rational part and the logarithmic part of the function. ### Step-by-Step Solution 1. **Identify the Rational Part:** The rational part of the function is \( \frac{x}{16 - x^2} \). The denominator cannot be zero: \[ 16 - x^2 \neq 0 \] This gives us: \[ x^2 \neq 16 \implies x \neq 4 \quad \text{and} \quad x \neq -4 \] 2. **Identify the Logarithmic Part:** The logarithmic part of the function is \( \log_2(x^3 - 2x) \). The argument of the logarithm must be greater than zero: \[ x^3 - 2x > 0 \] Factor the expression: \[ x(x^2 - 2) > 0 \] This can be factored further: \[ x(x - \sqrt{2})(x + \sqrt{2}) > 0 \] 3. **Determine the Critical Points:** The critical points from the inequality \( x(x - \sqrt{2})(x + \sqrt{2}) = 0 \) are: \[ x = 0, \quad x = \sqrt{2}, \quad x = -\sqrt{2} \] 4. **Test Intervals:** We will test the sign of the expression in the intervals defined by the critical points: - Interval \( (-\infty, -\sqrt{2}) \) - Interval \( (-\sqrt{2}, 0) \) - Interval \( (0, \sqrt{2}) \) - Interval \( (\sqrt{2}, \infty) \) - **For \( x < -\sqrt{2} \):** Choose \( x = -3 \): \[ (-3)(-3 - \sqrt{2})(-3 + \sqrt{2}) > 0 \quad \text{(positive)} \] - **For \( -\sqrt{2} < x < 0 \):** Choose \( x = -1 \): \[ (-1)(-1 - \sqrt{2})(-1 + \sqrt{2}) < 0 \quad \text{(negative)} \] - **For \( 0 < x < \sqrt{2} \):** Choose \( x = 1 \): \[ (1)(1 - \sqrt{2})(1 + \sqrt{2}) < 0 \quad \text{(negative)} \] - **For \( x > \sqrt{2} \):** Choose \( x = 2 \): \[ (2)(2 - \sqrt{2})(2 + \sqrt{2}) > 0 \quad \text{(positive)} \] 5. **Combine the Results:** From the sign analysis, we find that \( x(x - \sqrt{2})(x + \sqrt{2}) > 0 \) holds in the intervals: \[ (-\infty, -\sqrt{2}) \quad \text{and} \quad (\sqrt{2}, \infty) \] 6. **Final Domain:** We must exclude \( x = 4 \) and \( x = -4 \) from the domain. Therefore, the domain of \( f(x) \) is: \[ (-\infty, -\sqrt{2}) \cup (-4, -\sqrt{2}) \cup (\sqrt{2}, 4) \cup (4, \infty) \] ### Final Answer: The domain of \( f(x) \) is: \[ (-\infty, -4) \cup (-\sqrt{2}, 0) \cup (\sqrt{2}, 4) \cup (4, \infty) \]
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