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2. Evaluate each of the following limits (a) \( \lim _{x \rightarrow 2} \frac{x^{2}-4}{x-2} \) (b) \( \lim _{x \rightarrow 0} \frac{(x+4)^{2}-16}{x} \) (c) \( \lim _{x \rightarrow 3} \frac{x^{3}-9 x}{3 x^{2}-6 x-9} \) 3. Evaluate each of the following limits (a) \( \lim _{x \rightarrow 0} \frac{\sqrt{x+1}-1}{x} \) (b) \( \lim _{x \rightarrow 2} \frac{\sqrt{x+2}-2}{x-2} \) (c) \( \lim _{x \rightarrow 1} \frac{\sqrt{x+3}-2}{x-1} \)

Ask by Gonzalez Delgado. in Zambia
Mar 21,2025

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**2. (a) The limit is 4.** **(b) The limit is 8.** **(c) The limit is 1.5.** **3. (a) The limit is 0.5.** **(b) The limit is 0.25.** **(c) The limit is 0.25.**

Solución

**2. (a) Evaluate \(\displaystyle \lim_{x \rightarrow 2} \frac{x^{2}-4}{x-2}\)** Factor the numerator as a difference of squares: \[ x^2 - 4 = (x-2)(x+2) \] Then \[ \frac{x^{2}-4}{x-2} = \frac{(x-2)(x+2)}{x-2} = x+2 \quad (x \neq 2) \] Taking the limit as \(x \rightarrow 2\), \[ \lim_{x \rightarrow 2} (x+2) = 2+2 = 4. \] --- **2. (b) Evaluate \(\displaystyle \lim_{x \rightarrow 0} \frac{(x+4)^{2}-16}{x}\)** Expand the numerator: \[ (x+4)^2 - 16 = (x^2 + 8x + 16) - 16 = x^2 + 8x. \] Factor out \(x\): \[ x^2 + 8x = x(x+8). \] Thus, \[ \frac{(x+4)^{2}-16}{x} = \frac{x(x+8)}{x} = x+8 \quad (x \neq 0). \] Taking the limit as \(x \rightarrow 0\), \[ \lim_{x \rightarrow 0} (x+8) = 0+8 = 8. \] --- **2. (c) Evaluate \(\displaystyle \lim_{x \rightarrow 3} \frac{x^{3}-9 x}{3 x^{2}-6 x-9}\)** Factor the numerator: \[ x^3 - 9x = x(x^2 - 9) = x(x-3)(x+3). \] Factor the denominator. First, factor out \(3\): \[ 3x^2 - 6x - 9 = 3(x^2 - 2x - 3). \] Factor the quadratic: \[ x^2 - 2x - 3 = (x-3)(x+1). \] Thus, the denominator becomes: \[ 3(x-3)(x+1). \] Cancelling the common factor \((x-3)\) (valid for \(x \neq 3\)): \[ \frac{x(x-3)(x+3)}{3(x-3)(x+1)} = \frac{x(x+3)}{3(x+1)}. \] Taking the limit as \(x \rightarrow 3\): \[ \lim_{x \rightarrow 3} \frac{x(x+3)}{3(x+1)} = \frac{3(3+3)}{3(3+1)} = \frac{3 \times 6}{3 \times 4} = \frac{18}{12} = \frac{3}{2}. \] --- **3. (a) Evaluate \(\displaystyle \lim_{x \rightarrow 0} \frac{\sqrt{x+1}-1}{x}\)** Multiply numerator and denominator by the conjugate \(\sqrt{x+1}+1\): \[ \frac{\sqrt{x+1}-1}{x} \cdot \frac{\sqrt{x+1}+1}{\sqrt{x+1}+1} = \frac{(x+1)-1}{x(\sqrt{x+1}+1)} = \frac{x}{x(\sqrt{x+1}+1)} = \frac{1}{\sqrt{x+1}+1}. \] Taking the limit as \(x \rightarrow 0\): \[ \lim_{x \rightarrow 0} \frac{1}{\sqrt{x+1}+1} = \frac{1}{\sqrt{0+1}+1} = \frac{1}{1+1} = \frac{1}{2}. \] --- **3. (b) Evaluate \(\displaystyle \lim_{x \rightarrow 2} \frac{\sqrt{x+2}-2}{x-2}\)** Multiply the expression by the conjugate of the numerator: \[ \frac{\sqrt{x+2}-2}{x-2} \cdot \frac{\sqrt{x+2}+2}{\sqrt{x+2}+2} = \frac{(x+2)-4}{(x-2)(\sqrt{x+2}+2)} = \frac{x-2}{(x-2)(\sqrt{x+2}+2)} = \frac{1}{\sqrt{x+2}+2}. \] Taking the limit as \(x \rightarrow 2\): \[ \lim_{x \rightarrow 2} \frac{1}{\sqrt{x+2}+2} = \frac{1}{\sqrt{2+2}+2} = \frac{1}{\sqrt{4}+2} = \frac{1}{2+2} = \frac{1}{4}. \] --- **3. (c) Evaluate \(\displaystyle \lim_{x \rightarrow 1} \frac{\sqrt{x+3}-2}{x-1}\)** Multiply numerator and denominator by the conjugate: \[ \frac{\sqrt{x+3}-2}{x-1} \cdot \frac{\sqrt{x+3}+2}{\sqrt{x+3}+2} = \frac{(x+3)-4}{(x-1)(\sqrt{x+3}+2)} = \frac{x-1}{(x-1)(\sqrt{x+3}+2)} = \frac{1}{\sqrt{x+3}+2}. \] Taking the limit as \(x \rightarrow 1\): \[ \lim_{x \rightarrow 1} \frac{1}{\sqrt{x+3}+2} = \frac{1}{\sqrt{1+3}+2} = \frac{1}{\sqrt{4}+2} = \frac{1}{2+2} = \frac{1}{4}. \]

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To solve the limits provided, let's break down each one step by step. 2. (a) \( \lim _{x \rightarrow 2} \frac{x^{2}-4}{x-2} \) Here, both the numerator and denominator approach zero as \( x \) approaches 2, leading us to apply L'Hôpital's rule or factor the expression. Factoring gives us: \[ \frac{(x-2)(x+2)}{x-2} \] Canceling \( x-2 \) (provided \( x \neq 2 \)), we get: \[ \lim_{x \rightarrow 2} (x + 2) = 4. \] (b) \( \lim _{x \rightarrow 0} \frac{(x+4)^{2}-16}{x} \) Substituting \( x = 0 \) gives an indeterminate form \( \frac{0}{0} \). We can expand the numerator: \[ (x+4)^{2} - 16 = x^{2} + 8x + 16 - 16 = x^{2} + 8x. \] Thus, \[ \frac{x^{2} + 8x}{x} = x + 8. \] Taking the limit: \[ \lim_{x \rightarrow 0} (x + 8) = 8. \] (c) \( \lim _{x \rightarrow 3} \frac{x^{3}-9 x}{3 x^{2}-6 x-9} \) Evaluating directly leads to: \[ \frac{0}{0} \] Applying L'Hôpital's rule: The derivative of the numerator \( 3x^2 - 9 \) and of the denominator \( 6x - 6 \): \[ \lim_{x \rightarrow 3} \frac{3x^2 - 9}{6x - 6} = \frac{27 - 9}{18 - 6} = \frac{18}{12} = \frac{3}{2}. \] 3. (a) \( \lim _{x \rightarrow 0} \frac{\sqrt{x+1}-1}{x} \) This again leads to \( \frac{0}{0} \). We can rationalize the numerator: \[ \frac{(\sqrt{x+1}-1)(\sqrt{x+1}+1)}{x(\sqrt{x+1}+1)} = \frac{x}{x(\sqrt{x+1}+1)} = \frac{1}{\sqrt{x+1}+1}. \] Evaluating the limit: \[ \lim_{x \rightarrow 0} \frac{1}{\sqrt{1}+1} = \frac{1}{2}. \] (b) \( \lim _{x \rightarrow 2} \frac{\sqrt{x+2}-2}{x-2} \) This limit also gives \( \frac{0}{0} \). Rationalizing the numerator yields: \[ \frac{(\sqrt{x+2}-2)(\sqrt{x+2}+2)}{(x-2)(\sqrt{x+2}+2)} = \frac{x-2}{(x-2)(\sqrt{x+2}+2)} = \frac{1}{\sqrt{x+2}+2}. \] Taking the limit, we find: \[ \lim_{x \rightarrow 2} \frac{1}{\sqrt{4}+2} = \frac{1}{4}. \] (c) \( \lim _{x \rightarrow 1} \frac{\sqrt{x+3}-2}{x-1} \) We get \( \frac{0}{0} \) again: Rationalizing: \[ \frac{(\sqrt{x+3}-2)(\sqrt{x+3}+2)}{(x-1)(\sqrt{x+3}+2)} = \frac{x+3-4}{(x-1)(\sqrt{x+3}+2)} = \frac{x-1}{(x-1)(\sqrt{x+3}+2)} = \frac{1}{\sqrt{x+3}+2}. \] Taking the limit: \[ \lim_{x \rightarrow 1} \frac{1}{\sqrt{4}+2} = \frac{1}{4}. \]

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