Chapter 2: Problem 47
Prove the limit statements in Exercises 37-50. $$\lim _{x \rightarrow 1} f(x)=2 \quad \text { if } \quad f(x)=\left\\{\begin{array}{ll}{4-2 x,} & {x<1} \\ {6 x-4,} & {x \geq 1}\end{array}\right.$$
Short Answer
Expert verified
The limit is \( \lim_{x \to 1} f(x) = 2 \).
Step by step solution
01
Examine the Function and Its Definition
For the given piecewise function \( f(x) \), we have two parts: - \( f(x) = 4 - 2x \) when \( x < 1\) - \( f(x) = 6x - 4 \) when \( x \geq 1\).To prove the limit, we need to ensure that as \( x \) approaches 1 from both sides, the function approaches the same value, which is 2.
02
Calculate the Left-Sided Limit
For \( x < 1 \), substitute into the first part of the function: \( f(x) = 4 - 2x \).We need to find \( \lim_{x \to 1^-} f(x) \):\[\lim_{x \to 1^-} (4 - 2x) = 4 - 2(1) = 2\] Thus, the left-sided limit as \( x \) approaches 1 is 2.
03
Calculate the Right-Sided Limit
For \( x \geq 1 \), use the second part of the function: \( f(x) = 6x - 4 \).The right-sided limit is:\[\lim_{x \to 1^+} (6x - 4) = 6(1) - 4 = 2\]The right-sided limit as \( x \) approaches 1 is also 2.
04
Conclude the Limit Statement
Since the left-sided limit (2) and right-sided limit (2) are equal, we can conclude:\[\lim_{x \to 1} f(x) = 2\]Both sides approaching 2 confirms that the limit exists and equals 2.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Piecewise Functions
A piecewise function is a function composed of multiple sub-functions, each of which applies to a specific interval of the domain. These functions are represented in smaller segments rather than a single equation throughout. This type of function is useful when different rules need to be applied for different parts of the input. For example, the provided function has two parts:
- For all values of \( x < 1 \), the function follows the rule \( f(x) = 4 - 2x \).
- For values of \( x \geq 1 \), the function changes to \( f(x) = 6x - 4 \).
Exploring Left-Sided Limits
The left-sided limit of a function at a specific point focuses on approaching the point from the left side on the number line. To find this limit, we consider the values of \( x \) that are slightly less than the point of interest. In this exercise, we calculate \( \lim_{x \to 1^-} f(x) \) using the sub-function that applies when \( x < 1 \), which is \( f(x) = 4 - 2x \). This gives:\[\lim_{x \to 1^-} (4 - 2x) = 4 - 2(1) = 2\]Thus, as \( x \) approaches 1 from the left, the function value gets closer to 2. This calculation helps us understand the behavior of the function immediately before reaching the point \( x = 1 \).
Understanding Right-Sided Limits
The right-sided limit examines the values of \( x \) as they approach a point from the right side. In this case, we look at \( x \geq 1 \), which means considering \( x \) values slightly more than the point in question. For the given problem, the relevant part of the function is \( f(x) = 6x - 4 \). Therefore, we calculate:\[\lim_{x \to 1^+} (6x - 4) = 6(1) - 4 = 2\]This shows that as \( x \) approaches 1 from the right, the function's value also approaches 2. Calculating this limit informs us about the behavior of the function just after crossing the point \( x = 1 \).
Exploring Continuity
Continuity at a point in a function occurs when the following three conditions are met:
- The function is defined at the point.
- The left-sided limit and right-sided limit at that point are the same.
- The common limit value equals the function value at the point.