Question
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(c) Let \( f(x)=\frac{2 x+12}{x+6} \) (i) \( \lim _{x \rightarrow 6^{+}} f(x) \) (ii) \( \lim _{x \rightarrow 6^{-}} f(x) \) (iii) Use (i) and (ii) to deduce \( \lim f(x) \) at \( x=6 \).

Ask by Delgado Chambers. in South Africa
Jan 23,2025

Real Tutor Solution

Tutor-Verified Answer

Answer

All three limits are equal to 2.

Solution

Let's analyze the function \( f(x) = \frac{2x + 12}{x + 6} \) as \( x \) approaches 6. ### Simplifying the Function First, simplify \( f(x) \): \[ f(x) = \frac{2x + 12}{x + 6} = \frac{2(x + 6)}{x + 6} \] For all \( x \neq -6 \), we can cancel out \( x + 6 \): \[ f(x) = 2 \] This simplification shows that \( f(x) \) is a constant function equal to 2 for all \( x \) except \( x = -6 \), where the function is undefined. ### (i) \( \lim_{x \to 6^{+}} f(x) \) As \( x \) approaches 6 from the right (\( x \to 6^{+} \)), the function \( f(x) \) remains: \[ f(x) = 2 \] Thus, \[ \lim_{x \to 6^{+}} f(x) = 2 \] ### (ii) \( \lim_{x \to 6^{-}} f(x) \) Similarly, as \( x \) approaches 6 from the left (\( x \to 6^{-} \)), the function \( f(x) \) is still: \[ f(x) = 2 \] So, \[ \lim_{x \to 6^{-}} f(x) = 2 \] ### (iii) Deduce \( \lim_{x \to 6} f(x) \) Since both the right-hand limit and the left-hand limit as \( x \) approaches 6 are equal to 2, the overall limit exists and is equal to 2. \[ \lim_{x \to 6} f(x) = 2 \] **Final Answer:** All three limits are equal to two. Specifically, (i) 2, (ii) 2, and therefore (iii) limₓ→6 f (x ) = 2.

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Extra Insights

To evaluate the limits: (i) To compute \( \lim _{x \rightarrow 6^{+}} f(x) \): We substitute values of \( x \) approaching \( 6 \) from the right. Directly plugging in, we have: \[ f(6) = \frac{2(6) + 12}{6 + 6} = \frac{12 + 12}{12} = \frac{24}{12} = 2. \] Thus, \( \lim _{x \rightarrow 6^{+}} f(x) = 2. \) (ii) For \( \lim _{x \rightarrow 6^{-}} f(x) \): Similar to part (i), we substitute values of \( x \) approaching \( 6 \) from the left. Directly plugging in gives us: \[ f(6) = \frac{2(6) + 12}{6 + 6} = \frac{24}{12} = 2. \] Therefore, \( \lim _{x \rightarrow 6^{-}} f(x) = 2. \) (iii) Since both one-sided limits exist and are equal: \[ \lim_{x \rightarrow 6^{+}} f(x) = 2 \quad \text{and} \quad \lim_{x \rightarrow 6^{-}} f(x) = 2, \] we can conclude that: \[ \lim_{x \rightarrow 6} f(x) = 2. \]

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