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Suppose that the function \( f \) is defined, for all real numbers, as follows. \[ f(x)=\left\{\begin{array}{cc}-2 x+3 & \text { if } x<2 \\ x-3 & \text { if } x \geq 2\end{array}\right. \] Graph the function \( f \). Then determine whether or not the function is continuous

Ask by Peterson Weston. in the United States
Feb 03,2025

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Answer

The function \( f(x) \) is continuous for all real numbers.

Solution

To analyze the function \( f \) defined by \[ f(x) = \begin{cases} -2x + 3 & \text{if } x < 2, \\ x - 3 & \text{if } x \geq 2, \end{cases} \] let's break down its components, graph the function, and determine its continuity. ## Graphing the Function \( f \) The function \( f \) is piecewise-defined with two linear segments. Here's how each part behaves: 1. **For \( x < 2 \):** \[ f(x) = -2x + 3 \] - **Slope:** -2 (indicates the line is decreasing). - **Y-intercept:** 3 (the point where the line crosses the y-axis). - **Key Point:** When \( x = 2 \), \( f(2) = -2(2) + 3 = -1 \). However, since this piece is only for \( x < 2 \), the point \( (2, -1) \) is not included in this segment. 2. **For \( x \geq 2 \):** \[ f(x) = x - 3 \] - **Slope:** 1 (indicates the line is increasing). - **Y-intercept:** -3. - **Key Point:** At \( x = 2 \), \( f(2) = 2 - 3 = -1 \). This point **is** included in this segment. ### Plotting the Segments - **First Segment (\( x < 2 \)):** - Starts from the y-intercept at (0, 3). - Passes through the point \( (2, -1) \) but does not include it (usually represented with an open circle). - **Second Segment (\( x \geq 2 \)):** - Starts at \( (2, -1) \) (solid dot) since \( x = 2 \) is included. - Extends infinitely to the right with a slope of 1. ### Visual Representation While I can't draw the graph here, you can visualize it as follows: - **Left Line (\( x < 2 \)):** A straight line descending from the left, passing through (0, 3) and approaching \( (2, -1) \) with an open circle at \( (2, -1) \). - **Right Line (\( x \geq 2 \)):** A straight line ascending from \( (2, -1) \) onwards. ![Graph of the function f(x)](https://i.imgur.com/YourImageLink.png) *Note: Replace the URL with an actual graph image if available.* ## Determining Continuity A function is **continuous** at a point \( x = c \) if the following three conditions are met: 1. **\( f(c) \) is defined.** 2. **The limit \( \lim_{x \to c} f(x) \) exists.** 3. **\( \lim_{x \to c} f(x) = f(c) \).** Let's examine the point \( x = 2 \), where the definition of \( f(x) \) changes. 1. **\( f(2) \) is defined:** \[ f(2) = 2 - 3 = -1 \] 2. **Left-hand limit as \( x \) approaches 2:** \[ \lim_{x \to 2^-} f(x) = \lim_{x \to 2^-} (-2x + 3) = -2(2) + 3 = -1 \] 3. **Right-hand limit as \( x \) approaches 2:** \[ \lim_{x \to 2^+} f(x) = \lim_{x \to 2^+} (x - 3) = 2 - 3 = -1 \] Since both one-sided limits exist and are equal to each other and to \( f(2) \), the function \( f \) is **continuous at \( x = 2 \)**. Moreover, each piece of \( f \) is a linear function, which is continuous everywhere on its domain. Therefore, the entire function \( f \) is **continuous for all real numbers**. ## Conclusion - **Graph:** The function consists of two straight lines: - A decreasing line \( -2x + 3 \) for \( x < 2 \), - An increasing line \( x - 3 \) for \( x \geq 2 \), - Both segments meet seamlessly at \( (2, -1) \). - **Continuity:** \( f(x) \) is **continuous for all real numbers**.

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To graph the piecewise function \( f(x) \), we’ll break it down into two parts based on the defined intervals: 1. For \( x < 2 \), the function is given by \( f(x) = -2x + 3 \). This is a line with a slope of -2 that intersects the y-axis at (0, 3). For \( x < 2 \), you can plot points like \( f(0) = 3 \), \( f(1) = 1 \), and \( f(2) \) (though it won't be included in this part of the graph). 2. For \( x \geq 2 \), the function is defined as \( f(x) = x - 3 \). This is another line with a slope of 1 that intersects the y-axis at (0, -3). You can plot points like \( f(2) = -1 \), \( f(3) = 0 \), and so on. When you put these two parts together, you will see that the graph consists of two linear pieces: one decreasing line segment for \( x < 2 \) and another increasing line segment starting from \( x = 2 \). To check for continuity, we need to see if the function is continuous at the point where the definitions change, \( x = 2 \): 1. Evaluate \( f(2) = 2 - 3 = -1 \). 2. Check the limit from the left as \( x \) approaches 2: \( \lim_{x \to 2^-} f(x) = -2(2) + 3 = -1 \). 3. Check the limit from the right as \( x \) approaches 2: \( \lim_{x \to 2^+} f(x) = 2 - 3 = -1 \). Since the left limit, right limit, and the function value at \( x = 2 \) are all equal to -1, \( f(x) \) is continuous everywhere, including at \( x = 2 \). Therefore, the function is continuous.

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