Pregunta
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5. Consider \( f(x)=\frac{4-x}{3+x} \). a. What are the asymptotes? b. What is the \( \lim _{x \rightarrow-3^{+}} f(x) \) ? c. What is the \( \lim _{x \rightarrow-3^{-}} f(x) \) ? d. What is the \( \lim _{x \rightarrow \infty} f(x) \) ?

Ask by Bird Davison. in the United States
Jan 26,2025

Solución de tutoría real

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**a.** Vertical asymptote at \( x = -3 \) and horizontal asymptote at \( y = -1 \). **b.** As \( x \) approaches \(-3\) from the right, \( f(x) \) approaches \( +\infty \). **c.** As \( x \) approaches \(-3\) from the left, \( f(x) \) approaches \( -\infty \). **d.** As \( x \) approaches infinity, \( f(x) \) approaches \(-1\).

Solución

Let's analyze the function \( f(x) = \frac{4 - x}{3 + x} \) step by step for each part of the question. ### a. Asymptotes **Vertical Asymptote:** Vertical asymptotes occur where the denominator is zero (and the numerator is not zero). Set the denominator equal to zero: \[ 3 + x = 0 \quad \Rightarrow \quad x = -3 \] **Vertical Asymptote:** \( x = -3 \) **Horizontal Asymptote:** For rational functions where the degree of the numerator and the denominator are the same, the horizontal asymptote is the ratio of the leading coefficients. Here, both numerator and denominator are degree 1: \[ \text{Leading coefficient of numerator} = -1 \quad (\text{from } -x) \] \[ \text{Leading coefficient of denominator} = 1 \quad (\text{from } x) \] \[ \text{Horizontal Asymptote}: y = \frac{-1}{1} = -1 \] **Horizontal Asymptote:** \( y = -1 \) ### b. \( \lim_{{x \to -3^{+}}} f(x) \) We evaluate the limit as \( x \) approaches \(-3\) from the right (values greater than \(-3\)). \[ f(x) = \frac{4 - x}{3 + x} \] As \( x \to -3^+ \): - **Numerator:** \( 4 - (-3) = 7 \) (approaches 7) - **Denominator:** \( 3 + (-3^+) \) approaches \( 0^+ \) (a small positive number) \[ \lim_{{x \to -3^{+}}} f(x) = \frac{7}{0^+} = +\infty \] ### c. \( \lim_{{x \to -3^{-}}} f(x) \) We evaluate the limit as \( x \) approaches \(-3\) from the left (values less than \(-3\)). \[ f(x) = \frac{4 - x}{3 + x} \] As \( x \to -3^- \): - **Numerator:** \( 4 - (-3) = 7 \) (approaches 7) - **Denominator:** \( 3 + (-3^-) \) approaches \( 0^- \) (a small negative number) \[ \lim_{{x \to -3^{-}}} f(x) = \frac{7}{0^-} = -\infty \] ### d. \( \lim_{{x \to \infty}} f(x) \) For the limit as \( x \) approaches infinity, we analyze the leading terms. \[ f(x) = \frac{4 - x}{3 + x} = \frac{-x + 4}{x + 3} \] Divide numerator and denominator by \( x \): \[ f(x) = \frac{-1 + \frac{4}{x}}{1 + \frac{3}{x}} \] As \( x \to \infty \): - \( \frac{4}{x} \to 0 \) - \( \frac{3}{x} \to 0 \) \[ \lim_{{x \to \infty}} f(x) = \frac{-1 + 0}{1 + 0} = -1 \] **Final Answer:** **a.** The graph has a vertical asymptote at \( x = -3 \) and a horizontal asymptote at \( y = -1 \). **b.** \( \displaystyle \lim_{x \to -3^{+}} f(x) = +\infty \) **c.** \( \displaystyle \lim_{x \to -3^{-}} f(x) = -\infty \) **d.** \( \displaystyle \lim_{x \to \infty} f(x) = -1 \)

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The Deep Dive

To dive into the fascinating world of the function \( f(x) = \frac{4-x}{3+x} \), let’s look at its asymptotes! The vertical asymptote occurs where the denominator is zero, which is at \( x = -3 \). For the horizontal asymptote, we're interested in the behavior as \( x \) approaches infinity. As \( x \) grows very large, the function simplifies to \( f(x) \approx -1 \). So, the asymptotes are: - Vertical asymptote at \( x = -3 \) - Horizontal asymptote at \( y = -1 \) Now, let's tackle those limits! For \( \lim_{x \rightarrow -3^{+}} f(x) \), as we approach -3 from the right, the denominator becomes a very small positive number, while the numerator approaches \( 7 \). Thus, the limit tends to \( +\infty \). Conversely, for \( \lim_{x \rightarrow -3^{-}} f(x) \), approaching -3 from the left gives us a very small negative number in the denominator. This leads the limit to \( -\infty \). Lastly, for \( \lim_{x \rightarrow \infty} f(x) \), both the numerator and denominator are dominated by the respective \( -x \) and \( x \) terms, simplifying our limit to \( -1 \) as mentioned before. Overall, the limits reveal some fun and wild behavior near our asymptote!

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