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)=1−x2+4x+3x+13 and asked to find its domain and discuss its continuity at a=2.
We are also given the function g(x)=⌊4x2−36⌋2x+3−1 and asked to find its domain and discuss its continuity at a=−23. Here, ⌊x⌋ represents the greatest integer less than or equal to x.
2. Solution Steps
1.1.a) Domain of f(x):
For f(x) to be defined, we need two conditions:
(1) The expression inside the square root must be non-negative: 1−x2+4x+3x+13≥0.
(2) The denominator of the fraction must be non-zero: x2+4x+3=0.
First, consider the denominator: x2+4x+3=(x+1)(x+3).
So, x=−1 and x=−3.
Next, consider the expression inside the square root:
1−x2+4x+3x+13≥0
x2+4x+3x2+4x+3−(x+13)≥0
x2+4x+3x2+3x−10≥0
(x+1)(x+3)(x+5)(x−2)≥0
We can analyze the sign of this expression using a number line. The critical points are x=−5,−3,−1,2.
- x<−5: All factors are negative, so the expression is positive.
- −5<x<−3: (x+5) is positive, the rest are negative, so the expression is negative.
- −3<x<−1: (x+5) and (x+3) are positive, the rest are negative, so the expression is positive.
- −1<x<2: (x+5), (x+3) and (x+1) are positive, (x−2) is negative, so the expression is negative.
- x>2: All factors are positive, so the expression is positive.
Thus, the solution to the inequality is x∈(−∞,−5]∪(−3,−1)∪[2,∞).
So, the domain of f(x) is (−∞,−5]∪(−3,−1)∪[2,∞).
1.1.b) Continuity of f(x) at a=2:
Since 2 is in the domain of f(x), we need to check if f(2) is defined, if limx→2f(x) exists, and if limx→2f(x)=f(2).