Is the following piecewise defined function f(x) continuous at x = = 0, [cos(x), x≤0 f(x) = x²+x+1, x>0 ?

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### Continuity of a Piecewise Function

**Question:**
Is the following piecewise defined function \( f(x) \) continuous at \( x = 0 \)?
\[ f(x) = \begin{cases} 
\cos(x), & x \leq 0 \\
x^2 + x + 1, & x > 0 
\end{cases} \]

Please briefly explain your answer (in 4 sentences or fewer, if possible). Hint: What are the criteria for a function to be continuous at a point \( x_0 \)? 

**Explanation:**
For a function to be continuous at a point \( x_0 \), the following three criteria must be satisfied:
1. \( f(x_0) \) is defined.
2. \( \lim_{{x \to x_0}} f(x) \) exists.
3. \( \lim_{{x \to x_0}} f(x) = f(x_0) \).

To determine the continuity at \( x = 0 \):
- Find \( f(0) \) from the piecewise definition, which is \( \cos(0) = 1 \).
- Calculate the left-hand limit: \( \lim_{{x \to 0^-}} \cos(x) = \cos(0) = 1 \).
- Calculate the right-hand limit: \( \lim_{{x \to 0^+}} (x^2 + x + 1) = 1^2 + 0 + 1 = 1 \).

Since all three criteria are satisfied, the function \( f(x) \) is continuous at \( x = 0 \).
Transcribed Image Text:### Continuity of a Piecewise Function **Question:** Is the following piecewise defined function \( f(x) \) continuous at \( x = 0 \)? \[ f(x) = \begin{cases} \cos(x), & x \leq 0 \\ x^2 + x + 1, & x > 0 \end{cases} \] Please briefly explain your answer (in 4 sentences or fewer, if possible). Hint: What are the criteria for a function to be continuous at a point \( x_0 \)? **Explanation:** For a function to be continuous at a point \( x_0 \), the following three criteria must be satisfied: 1. \( f(x_0) \) is defined. 2. \( \lim_{{x \to x_0}} f(x) \) exists. 3. \( \lim_{{x \to x_0}} f(x) = f(x_0) \). To determine the continuity at \( x = 0 \): - Find \( f(0) \) from the piecewise definition, which is \( \cos(0) = 1 \). - Calculate the left-hand limit: \( \lim_{{x \to 0^-}} \cos(x) = \cos(0) = 1 \). - Calculate the right-hand limit: \( \lim_{{x \to 0^+}} (x^2 + x + 1) = 1^2 + 0 + 1 = 1 \). Since all three criteria are satisfied, the function \( f(x) \) is continuous at \( x = 0 \).
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