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Find the critical numbers, the intervals on which \( f(x) \) is increasing, the inte \( f(x)=\frac{x^{2}}{x-5} \) B. There is no solution. Select the correct choice below and, if necessary, fit in the answer box to A. The function is decreasing on \( (-\infty 0,0),(10, \infty) \), (Type your answer using interval nolation. Uso a comma to separa B. There is no solution. Which statement regarding the local extrema of the function is true? A. The function has a local minimum al \( x=0 \) and a local maximum at B. The function has a local minimum al \( x=10 \) and a local maximum C. The function has no local extrema.

Ask by Conner Burton. in the United States
Mar 10,2025

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Answer

The function \( f(x) = \frac{x^2}{x-5} \) has critical numbers at \( x=0 \) and \( x=10 \). It is increasing on \( (-\infty,0) \) and \( (10,\infty) \), and decreasing on \( (0,5) \) and \( (5,10) \). The function has a local maximum at \( x=0 \) and a local minimum at \( x=10 \).

Solution

We begin with \[ f(x)=\frac{x^2}{x-5}, \] with domain all real numbers except \( x=5 \). 1. **Finding the critical numbers**  a. Find \( f'(x) \) using the quotient rule. Recall that if \[ f(x)=\frac{g(x)}{h(x)}, \] then \[ f'(x)=\frac{g'(x)h(x)-g(x)h'(x)}{[h(x)]^2}. \]  b. Here, \( g(x)=x^2 \) and \( h(x)=x-5 \). Then, \[ g'(x)=2x \quad \text{and} \quad h'(x)=1. \]  c. Applying the quotient rule, we have \[ f'(x)=\frac{(2x)(x-5)-x^2(1)}{(x-5)^2} = \frac{2x(x-5)- x^2}{(x-5)^2}. \]  d. Expand the numerator: \[ 2x(x-5)=2x^2-10x, \] so \[ f'(x)=\frac{2x^2-10x-x^2}{(x-5)^2}=\frac{x^2-10x}{(x-5)^2}. \]  e. Factor the numerator: \[ x^2-10x=x(x-10). \] Thus, \[ f'(x)=\frac{x(x-10)}{(x-5)^2}. \]  f. Critical numbers occur when \( f'(x)=0 \) or is undefined (provided the point is in the domain). The numerator is zero when \[ x(x-10)=0, \] so \( x=0 \) or \( x=10 \). The derivative is undefined when the denominator is zero, i.e. when \[ (x-5)^2=0 \quad\Rightarrow\quad x=5. \] However, since \( f(x) \) is not defined at \( x=5 \) (vertical asymptote), we do not consider \( x=5 \) as a critical number.  g. Therefore, the critical numbers are \[ x=0 \quad \text{and} \quad x=10. \] 2. **Determining the intervals on which \( f(x) \) is increasing** Since \[ f'(x)=\frac{x(x-10)}{(x-5)^2}, \] and \( (x-5)^2 \) is always positive for \( x\neq5 \), the sign of \( f'(x) \) is determined by the numerator \( x(x-10) \).  a. Identify the zeros of the numerator: \[ x=0 \quad \text{and} \quad x=10. \]  b. Test intervals determined by these values (and taking care of the vertical asymptote at \( x=5 \)):   • For \( x<0 \) (for example, \( x=-1 \)):    \( (-1)\cdot((-1)-10) = (-1)\cdot(-11) = 11 > 0 \).    Thus, \( f'(x)>0 \) and \( f(x) \) is increasing on \( (-\infty,0) \).   • For \( 010 \) (for example, \( x=11 \)):    \( 11\cdot(11-10)=11\cdot(1)=11 > 0 \).    Thus, \( f(x) \) is increasing on \( (10,\infty) \).  c. Therefore, the function is increasing on \[ (-\infty,0) \quad \text{and} \quad (10,\infty). \] 3. **Local extrema**  a. At \( x=0 \):   - For \( x<0 \), \( f'(x)>0 \) (increasing).   - For \( 010 \), \( f'(x)>0 \) (increasing).   Thus, \( f(x) \) has a local minimum at \( x=10 \).   The function value is \[ f(10)=\frac{10^2}{10-5}=\frac{100}{5}=20. \] 4. **Answering the Multiple-Choice Statement** The statements provided are: - A. The function has a local minimum at \( x=0 \) and a local maximum at \(\dots\) - B. The function has a local minimum at \( x=10 \) and a local maximum at \( x=0 \). - C. The function has no local extrema. From our analysis, the correct statement is: \[ \textbf{B. The function has a local minimum at } x=10 \textbf{ and a local maximum at } x=0. \] 5. **Summary** - The critical numbers of \( f(x)=\frac{x^2}{x-5} \) are \( x=0 \) and \( x=10 \). - \( f(x) \) is increasing on \( (-\infty,0) \) and \( (10,\infty) \). - \( f(x) \) is decreasing on \( (0,5) \) and \( (5,10) \). - \( f \) has a local maximum at \( x=0 \) (with \( f(0)=0 \)) and a local minimum at \( x=10 \) (with \( f(10)=20 \)).

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The Deep Dive

To find critical numbers of \( f(x) = \frac{x^2}{x-5} \), we set the derivative \( f'(x) \) to zero or look for points where it is undefined. This involves using the quotient rule, which reveals that the critical points occur at \( x = 0 \) and \( x = 10 \). The sign changes of the derivative around these points indicate that \( f(x) \) is increasing on intervals \( (-\infty, 0) \) and \( (10, \infty) \), and decreasing on \( (0, 10) \). For local extrema: both critical points, \( x = 0 \) and \( x = 10 \), lead to a change in the behavior of the function. At \( x = 0 \), there is a local minimum, and at \( x = 10 \), a local maximum occurs. So, the correct statement would be: "A. The function has a local minimum at \( x=0 \) and a local maximum at \( x=10 \)."

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