We are given a function $f(x) = \frac{x+1}{\lfloor 3x-2 \rfloor}$, where $\lfloor x \rfloor$ represents the greatest integer less than or equal to $x$. (a) We need to find the domain of $f(x)$. (b) We need to discuss the continuity of $f(x)$ at $x = -1$.

AnalysisDomainContinuityFloor FunctionLimits
2025/6/21

1. Problem Description

We are given a function f(x)=x+13x2f(x) = \frac{x+1}{\lfloor 3x-2 \rfloor}, where x\lfloor x \rfloor represents the greatest integer less than or equal to xx.
(a) We need to find the domain of f(x)f(x).
(b) We need to discuss the continuity of f(x)f(x) at x=1x = -1.

2. Solution Steps

(a) The domain of f(x)f(x) is the set of all real numbers xx for which the denominator is not zero.
Thus, we need to find the values of xx for which 3x20\lfloor 3x-2 \rfloor \ne 0.
3x2=0\lfloor 3x-2 \rfloor = 0 if and only if 03x2<10 \le 3x-2 < 1.
Adding 2 to each part of the inequality, we have 23x<32 \le 3x < 3.
Dividing by 3, we get 23x<1\frac{2}{3} \le x < 1.
Thus, the domain of f(x)f(x) is the set of all real numbers xx such that x[23,1)x \notin [\frac{2}{3}, 1).
In interval notation, the domain is (,23)[1,)(-\infty, \frac{2}{3}) \cup [1, \infty).
(b) To discuss the continuity of f(x)f(x) at x=1x = -1, we need to evaluate f(1)f(-1).
f(1)=1+13(1)2=05=05=0f(-1) = \frac{-1+1}{\lfloor 3(-1)-2 \rfloor} = \frac{0}{\lfloor -5 \rfloor} = \frac{0}{-5} = 0.
We need to check if limx1f(x)=f(1)=0\lim_{x \to -1} f(x) = f(-1) = 0.
For xx close to 1-1, say in the interval (1.5,0.5)(-1.5, -0.5), we have 3x23x-2 between 6.5-6.5 and 3.5-3.5.
Then 3x2\lfloor 3x-2 \rfloor is a constant, equal to 6-6.
limx1f(x)=limx1x+13x2=limx1x+15=1+15=05=0\lim_{x \to -1} f(x) = \lim_{x \to -1} \frac{x+1}{\lfloor 3x-2 \rfloor} = \lim_{x \to -1} \frac{x+1}{-5} = \frac{-1+1}{-5} = \frac{0}{-5} = 0.
Since limx1f(x)=f(1)=0\lim_{x \to -1} f(x) = f(-1) = 0, f(x)f(x) is continuous at x=1x = -1.

3. Final Answer

(a) The domain of f(x)f(x) is (,23)[1,)(-\infty, \frac{2}{3}) \cup [1, \infty).
(b) f(x)f(x) is continuous at x=1x = -1.

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