We are given the function $f(x) = \sqrt{1 - \frac{x+13}{x^2+4x+3}}$ and asked to find its domain and discuss its continuity at $a=2$. We are also given the function $g(x) = \frac{\sqrt{2x+3} - 1}{\lfloor 4x^2 - 36 \rfloor}$ and asked to find its domain and discuss its continuity at $a = -\frac{3}{2}$. Here, $\lfloor x \rfloor$ represents the greatest integer less than or equal to $x$.

AnalysisDomainContinuityFunctionsInequalitiesSquare RootGreatest Integer Function
2025/6/6

1. Problem Description

We are given the function f(x)=1x+13x2+4x+3f(x) = \sqrt{1 - \frac{x+13}{x^2+4x+3}} and asked to find its domain and discuss its continuity at a=2a=2.
We are also given the function g(x)=2x+314x236g(x) = \frac{\sqrt{2x+3} - 1}{\lfloor 4x^2 - 36 \rfloor} and asked to find its domain and discuss its continuity at a=32a = -\frac{3}{2}. Here, x\lfloor x \rfloor represents the greatest integer less than or equal to xx.

2. Solution Steps

1.1.a) Domain of f(x)f(x):
For f(x)f(x) to be defined, we need two conditions:
(1) The expression inside the square root must be non-negative: 1x+13x2+4x+301 - \frac{x+13}{x^2+4x+3} \geq 0.
(2) The denominator of the fraction must be non-zero: x2+4x+30x^2+4x+3 \neq 0.
First, consider the denominator: x2+4x+3=(x+1)(x+3)x^2+4x+3 = (x+1)(x+3).
So, x1x \neq -1 and x3x \neq -3.
Next, consider the expression inside the square root:
1x+13x2+4x+301 - \frac{x+13}{x^2+4x+3} \geq 0
x2+4x+3(x+13)x2+4x+30\frac{x^2+4x+3 - (x+13)}{x^2+4x+3} \geq 0
x2+3x10x2+4x+30\frac{x^2+3x-10}{x^2+4x+3} \geq 0
(x+5)(x2)(x+1)(x+3)0\frac{(x+5)(x-2)}{(x+1)(x+3)} \geq 0
We can analyze the sign of this expression using a number line. The critical points are x=5,3,1,2x=-5, -3, -1, 2.
- x<5x < -5: All factors are negative, so the expression is positive.
- 5<x<3-5 < x < -3: (x+5)(x+5) is positive, the rest are negative, so the expression is negative.
- 3<x<1-3 < x < -1: (x+5)(x+5) and (x+3)(x+3) are positive, the rest are negative, so the expression is positive.
- 1<x<2-1 < x < 2: (x+5)(x+5), (x+3)(x+3) and (x+1)(x+1) are positive, (x2)(x-2) is negative, so the expression is negative.
- x>2x > 2: All factors are positive, so the expression is positive.
Thus, the solution to the inequality is x(,5](3,1)[2,)x \in (-\infty, -5] \cup (-3, -1) \cup [2, \infty).
So, the domain of f(x)f(x) is (,5](3,1)[2,)(-\infty, -5] \cup (-3, -1) \cup [2, \infty).
1.1.b) Continuity of f(x)f(x) at a=2a=2:
Since 22 is in the domain of f(x)f(x), we need to check if f(2)f(2) is defined, if limx2f(x)\lim_{x \to 2} f(x) exists, and if limx2f(x)=f(2)\lim_{x \to 2} f(x) = f(2).
f(2)=12+1322+4(2)+3=1154+8+3=11515=11=0f(2) = \sqrt{1 - \frac{2+13}{2^2+4(2)+3}} = \sqrt{1 - \frac{15}{4+8+3}} = \sqrt{1 - \frac{15}{15}} = \sqrt{1-1} = 0.
Since the expression is defined at x=2x=2, and f(2)=0f(2) = 0, we need to evaluate limx2f(x)\lim_{x \to 2} f(x).
Since 2 is in the domain of f(x)f(x) and f(x)f(x) is constructed of continuous functions in its domain, we have limx2f(x)=f(2)=0\lim_{x \to 2} f(x) = f(2) = 0.
Therefore, f(x)f(x) is continuous at x=2x=2.
1.2.a) Domain of g(x)g(x):
For g(x)g(x) to be defined, we need two conditions:
(1) The expression inside the square root must be non-negative: 2x+302x+3 \geq 0, which implies x32x \geq -\frac{3}{2}.
(2) The denominator must be non-zero: 4x2360\lfloor 4x^2 - 36 \rfloor \neq 0.
This means 4x2364x^2 - 36 cannot be in the interval [0,1)[0, 1), or 04x236<10 \leq 4x^2 - 36 < 1.
This gives 364x2<3736 \leq 4x^2 < 37, so 9x2<374=9.259 \leq x^2 < \frac{37}{4} = 9.25.
This implies 9.25<x3- \sqrt{9.25} < x \leq -3 or 3x<9.253 \leq x < \sqrt{9.25}.
Thus xx cannot be in these intervals.
The domain of g(x)g(x) must satisfy x32x \geq -\frac{3}{2} and x[9.25,3][3,9.25]x \notin [-\sqrt{9.25}, -3] \cup [3, \sqrt{9.25}].
Since x32=1.5x \geq -\frac{3}{2} = -1.5, we only need to consider the condition x[3,9.25]x \notin [3, \sqrt{9.25}].
So, the domain of g(x)g(x) is [1.5,3)(9.25,)[-1.5, 3) \cup (\sqrt{9.25}, \infty).
1.2.b) Continuity of g(x)g(x) at a=32a = -\frac{3}{2}:
First, we evaluate g(32)g(-\frac{3}{2}).
g(32)=2(32)+314(32)236=3+314(94)36=01936=127=127=127g(-\frac{3}{2}) = \frac{\sqrt{2(-\frac{3}{2})+3} - 1}{\lfloor 4(-\frac{3}{2})^2 - 36 \rfloor} = \frac{\sqrt{-3+3}-1}{\lfloor 4(\frac{9}{4}) - 36 \rfloor} = \frac{0-1}{\lfloor 9-36 \rfloor} = \frac{-1}{\lfloor -27 \rfloor} = \frac{-1}{-27} = \frac{1}{27}.
Now let's discuss the right-hand limit, since x32x \geq -\frac{3}{2}:
limx32+g(x)=limx32+2x+314x236\lim_{x \to -\frac{3}{2}^+} g(x) = \lim_{x \to -\frac{3}{2}^+} \frac{\sqrt{2x+3}-1}{\lfloor 4x^2 - 36 \rfloor}.
As x32+x \to -\frac{3}{2}^+, 2x+310\sqrt{2x+3}-1 \to 0.
Also, as x32x \to -\frac{3}{2}, 4x2364(94)36=936=274x^2 - 36 \to 4(\frac{9}{4})-36 = 9-36 = -27.
Therefore, 4x23627\lfloor 4x^2 - 36 \rfloor \to -27 as x32x \to -\frac{3}{2}.
So, limx32+g(x)=0127=127\lim_{x \to -\frac{3}{2}^+} g(x) = \frac{0-1}{-27} = \frac{1}{27}.
Since limx32+g(x)=g(32)=127\lim_{x \to -\frac{3}{2}^+} g(x) = g(-\frac{3}{2}) = \frac{1}{27}, the function g(x)g(x) is right-continuous at x=32x=-\frac{3}{2}.

3. Final Answer

1.1.a) Domain of f(x)f(x): (,5](3,1)[2,)(-\infty, -5] \cup (-3, -1) \cup [2, \infty)
1.1.b) f(x)f(x) is continuous at x=2x=2.
1.2.a) Domain of g(x)g(x): [1.5,3)(9.25,)[-1.5, 3) \cup (\sqrt{9.25}, \infty)
1.2.b) g(x)g(x) is right-continuous at x=32x=-\frac{3}{2}.

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