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(1) Evaluate the following limits. State the asymptotes, if any: (i) \( \lim _{t \rightarrow 3} \frac{2-t}{-2 t^{2}+7 t-3} \) (ii) \( \lim _{x \rightarrow-\infty} \frac{x-\sqrt{x^{2}-x+1}}{2 x-\sqrt{4 x^{2}+5 x-1}} \)

Ask by Reid Schneider. in Canada
Jan 26,2025

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Answer

**Limits and Asymptotes:** 1. **Limit (i):** \[ \lim_{t \rightarrow 3} \frac{2 - t}{-2t^{2} + 7t - 3} \text{ does not exist.} \] **Asymptote:** Vertical asymptote at \( t = 3 \). 2. **Limit (ii):** \[ \lim_{x \rightarrow -\infty} \frac{x - \sqrt{x^{2} - x + 1}}{2x - \sqrt{4x^{2} + 5x - 1}} = \frac{1}{2}. \] **Asymptote:** Horizontal asymptote at \( y = \frac{1}{2} \).

Solution

Let's evaluate each limit and determine any asymptotes associated with them. --- **(i)** \[ \lim_{t \rightarrow 3} \frac{2 - t}{-2t^{2} + 7t - 3} \] **Step 1: Factor the Denominator** First, factor the quadratic in the denominator: \[ -2t^{2} + 7t - 3 = -(2t^{2} - 7t + 3) \] Factor \(2t^{2} - 7t + 3\): \[ 2t^{2} - 7t + 3 = (2t - 1)(t - 3) \] So, the denominator becomes: \[ -2t^{2} + 7t - 3 = -(2t - 1)(t - 3) \] **Step 2: Analyze the Limit** As \( t \rightarrow 3 \): - The **numerator**: \(2 - t \rightarrow -1\). - The **denominator**: \(-(2t - 1)(t - 3) \rightarrow -[(6 - 1)(0)] = 0\). Thus, the expression approaches \(\frac{-1}{0}\), suggesting a vertical asymptote at \( t = 3 \). **Step 3: Determine the Direction of the Asymptote** - **From the Right (\( t \rightarrow 3^+ \))**: - \( t - 3 \) is positive. - Denominator approaches \(0^+\). - The limit approaches \( \frac{-1}{0^+} = -\infty \). - **From the Left (\( t \rightarrow 3^- \))**: - \( t - 3 \) is negative. - Denominator approaches \(0^-\). - The limit approaches \( \frac{-1}{0^-} = +\infty \). **Conclusion for (i):** \[ \lim_{t \rightarrow 3} \frac{2 - t}{-2t^{2} + 7t - 3} \text{ does not exist because it approaches } +\infty \text{ from the left and } -\infty \text{ from the right.} \] **Asymptote:** There is a **vertical asymptote** at \( t = 3 \). --- **(ii)** \[ \lim_{x \rightarrow -\infty} \frac{x - \sqrt{x^{2} - x + 1}}{2x - \sqrt{4x^{2} + 5x - 1}} \] **Step 1: Simplify the Expression** For large \(|x|\), especially as \( x \rightarrow -\infty \): - **Numerator:** \[ x - \sqrt{x^{2} - x + 1} \approx x - (-x) \sqrt{1 - \frac{1}{x} + \frac{1}{x^{2}}} = x + x\left(1 - \frac{1}{2x} + \cdots\right) \approx 2x - \frac{1}{2} \] - **Denominator:** \[ 2x - \sqrt{4x^{2} + 5x - 1} \approx 2x - (-2x) \sqrt{1 + \frac{5}{4x} - \frac{1}{4x^{2}}} = 2x + 2x\left(1 + \frac{5}{8x} + \cdots\right) \approx 4x + \frac{5}{4} \] **Step 2: Compute the Limit** \[ \lim_{x \rightarrow -\infty} \frac{2x - \frac{1}{2}}{4x + \frac{5}{4}} = \lim_{x \rightarrow -\infty} \frac{2x}{4x} = \frac{1}{2} \] **Conclusion for (ii):** \[ \lim_{x \rightarrow -\infty} \frac{x - \sqrt{x^{2} - x + 1}}{2x - \sqrt{4x^{2} + 5x - 1}} = \frac{1}{2} \] **Asymptote:** There is a **horizontal asymptote** at \( y = \frac{1}{2} \). --- **Final Summary:** 1. **Limit (i):** \[ \lim_{t \rightarrow 3} \frac{2 - t}{-2t^{2} + 7t - 3} \text{ does not exist } (\text{approaches } +\infty \text{ from the left and } -\infty \text{ from the right}). \] **Asymptote:** Vertical asymptote at \( t = 3 \). 2. **Limit (ii):** \[ \lim_{x \rightarrow -\infty} \frac{x - \sqrt{x^{2} - x + 1}}{2x - \sqrt{4x^{2} + 5x - 1}} = \frac{1}{2}. \] **Asymptote:** Horizontal asymptote at \( y = \frac{1}{2} \).

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Let's evaluate the limits step by step, starting with the first one. (i) To find the limit \( \lim _{t \rightarrow 3} \frac{2-t}{-2t^{2}+7t-3} \), we first substitute \( t = 3 \) into the denominator: \[ -2(3^2) + 7(3) - 3 = -18 + 21 - 3 = 0. \] This gives us a \( 0 \) in the denominator. We then need to factor the denominator. The polynomial \( -2t^2 + 7t - 3 \) can be factored as follows: \[ -2t^2 + 7t - 3 = -(2t^2 - 7t + 3) = -(2t - 1)(t - 3). \] Thus, the limit can be rewritten as: \[ \lim_{t \rightarrow 3} \frac{2-t}{-(2t-1)(t-3)}. \] We can now cancel \( t - 3 \) in the numerator and denominator (noting that we are approaching \( t = 3 \), so we are not actually at 3): \[ = \lim_{t \rightarrow 3} \frac{2-t}{-(2t-1)} = \lim_{t \rightarrow 3} \frac{-(t-2)}{-(2t-1)} = \lim_{t \rightarrow 3} \frac{t-2}{2t-1}. \] Substituting \( t = 3 \): \[ = \frac{3-2}{2(3)-1} = \frac{1}{6-1} = \frac{1}{5}. \] Thus, the limit is \( \frac{1}{5} \) and we note that there is a vertical asymptote at \( t = 3 \) since the denominator equals zero there. (ii) Now we evaluate \( \lim _{x \rightarrow-\infty} \frac{x-\sqrt{x^{2}-x+1}}{2x-\sqrt{4x^{2}+5x-1}} \). To simplify for large negative \( x \), we factor out \( x \) from the square roots in both the numerator and denominator. In the numerator: \[ \sqrt{x^2 - x + 1} = \sqrt{x^2(1 - \frac{1}{x} + \frac{1}{x^2})} = |x| \sqrt{1 - \frac{1}{x} + \frac{1}{x^2}} = -x\sqrt{1 - \frac{1}{x} + \frac{1}{x^2}} \text{ (as \( x \to -\infty \))}. \] Thus, we rewrite the numerator: \[ x - \sqrt{x^2 - x + 1} = x + x\sqrt{1 - \frac{1}{x} + \frac{1}{x^2}} = x(1 + \sqrt{1 - \frac{1}{x} + \frac{1}{x^2}}). \] In the denominator: \[ \sqrt{4x^2 + 5x - 1} = |2x|\sqrt{1 + \frac{5}{4x} - \frac{1}{4x^2}} = -2x \sqrt{1 + \frac{5}{4x} - \frac{1}{4x^2}}. \] Thus, the denominator becomes: \[ 2x - \sqrt{4x^2 + 5x - 1} = 2x + 2x\sqrt{1 + \frac{5}{4x} - \frac{1}{4x^2}} = 2x(1 + \sqrt{1 + \frac{5}{4x} - \frac{1}{4x^2}}). \] Now we can simplify the limit: \[ \lim_{x \rightarrow -\infty} \frac{x(1 + \sqrt{1 - \frac{1}{x} + \frac{1}{x^2}})}{2x(1 + \sqrt{1 + \frac{5}{4x} - \frac{1}{4x^2}})} = \lim_{x \rightarrow -\infty} \frac{1 + \sqrt{1 - \frac{1}{x} + \frac{1}{x^2}}}{2(1 + \sqrt{1 + \frac{5}{4x} - \

Related Questions

Multiple Choice Identify the choice that best completes the statement or answers the question. Find any points of discontinuity for the rational function. 1. \( y=\frac{(x-7)(x+2)(x-9)}{(x-5)(x-2)} \) a. \( x=-5, x=-2 \) b. \( x=5, x=2 \) c. \( x=-7, x=2, x=-9 \) d. \( x=7, x=-2, x=9 \) 2. \( y=\frac{(x+7)(x+4)(x+2)}{(x+5)(x-3)} \) a. \( x=-5, x=3 \) b. \( x=7, x=4, x=2 \) c. \( x=-7, x=-4, x=-2 \) d. \( x=5, x=-3 \) 3. \( y=\frac{x+4}{x^{2}+8 x+15} \) a. \( x=-5, x=-3 \) b. \( x=-4 \) c. \( x=-5, x=3 \) d. \( x=5, x=3 \) 4. \( y=\frac{x-3}{x^{2}+3 x-10} \) a. \( x=-5, x=2 \) b. \( x=5, x=-2 \) c. \( x=3 \) d. \( x \) \( =-5, x=-2 \) 6. What are the points of discontinuity? Are they all removable? \[ y=\frac{(x-4)}{x^{2}-13 x+36} \] a. \( x=-9, x=-4, x=8 \); yes b. \( x=1, x=8, x= \) -8; no c. \( x=9, x=4 \); no d. \( x=-9, x=-4 \); no 7. Describe the vertical asymptote(s) and hole(s) for the graph of \( y=\frac{(x-2)(x-5)}{(x-5)(x+2)} \). a. asymptote: \( x=2 \) and hole: \( x=-5 \) b. asymptotes: \( x=-2 \) and hole: \( x=-5 \) c. asymptote: \( x=-2 \) and hole: \( x=5 \) d. asymptote: \( x=-2 \) and hole: \( x=-2 \) a. \( x=-3, x=-8 \); no b. \( x=5, x=-7, x=1 \); no c. \( x=-5, x=7, x=-1 \); yes d. \( x=3, x=8 \); yes 8. Describe the vertical asymptote(s) and hole(s) for the graph of \( y=\frac{x+1}{x^{2}+6 x+5} \). a. asymptote: \( x=-1 \) and hole: \( x=-1 \) b. asymptote: \( x=-1 \) and hole: \( x=-1 \) c. asymptotes: \( x=-1,-1 \) and hole: \( x=-1 \) d. asymptote: -5 and hole: \( x=-1 \), 9. Find the horizontal asymptote of the graph of \( y=\frac{7 x^{6}+7 x+3}{9 x^{5}+7 x+3} \). a. \( y=0 \) b. \( y=\frac{7}{9} \) c. no horizontal asymptote d. \( y=\frac{6}{5} \)
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