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1. **Graph of \( f(x) = \frac{-6}{x+2} - 3 \):**
- **Vertical Asymptote:** \( x = -2 \)
- **Horizontal Asymptote:** \( y = -3 \)
- **Intercepts:**
- **Y-intercept:** \( (0, -6) \)
- **X-intercept:** \( (-4, 0) \)
- **Domain:** All real numbers except \( x = -2 \) (\( x \neq -2 \))
- **Range:** All real numbers except \( y = -3 \) (\( y \neq -3 \))
- **Symmetry:** No axis of symmetry, but it is symmetric under a 180° rotation about the point \( (-2, -3) \).
2. **Vertical Asymptote:** \( x = -2 \)
3. **Horizontal Asymptote:** \( y = -3 \)
4. **Domain:** \( x \neq -2 \) (\( x \in \mathbb{R} \setminus \{-2\} \))
5. **Range:** \( y \neq -3 \) (\( y \in \mathbb{R} \setminus \{-3\} \))
6. **Axes of Symmetry:** None
Solución
We are given
f(x) = (–6/(x + 2)) – 3.
Let’s answer each part one by one.
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(1) Sketch the graph of f
Step 1. Find basic features and transformations.
• Write f(x) = –6/(x + 2) – 3.
• Notice that the function is a transformed reciprocal function. Begin with y = 1/x, then multiply by –6 (which reflects it in the x‑axis and stretches it), then replace x by x + 2 (shifting the graph 2 units left), and finally subtract 3 (shifting the graph 3 units down).
Step 2. Identify the asymptotes.
• The vertical asymptote occurs when the denominator is zero, i.e. x + 2 = 0 ⟹ x = –2.
• The horizontal asymptote is found by considering x large; since –6/(x + 2) → 0 as x → ±∞, we have y → –3. Thus y = –3.
Step 3. Find intercepts.
• y‑intercept: Set x = 0.
f(0) = –6/(0 + 2) – 3 = –6/2 – 3 = –3 – 3 = –6.
So, the point is (0, –6).
• x‑intercept: Set f(x) = 0.
0 = –6/(x + 2) – 3 ⟹ –6/(x + 2) = 3 ⟹ x + 2 = –6/3 = –2 ⟹ x = –4.
So, the point is (–4, 0).
Step 4. Draw the graph.
• Sketch the vertical line x = –2 and the horizontal line y = –3.
• Plot the intercepts (0, –6) and (–4, 0).
• Draw the two branches of the hyperbola:
– One branch in the region x < –2 (to the left of the vertical asymptote), which approaches the asymptotes as x → –2⁻ and as x → –∞.
– The other branch in the region x > –2, approaching the asymptotes as x → –2⁺ and as x → +∞.
• Also note that the graph is a reflection (with a vertical stretch) and translation of the basic reciprocal graph y = 1/x.
A rough sketch is as follows:
y
| Branch: coming from below, rising toward the asymptotes
| (approaches y = –3 from below as x → +∞)
-- – – – – – – – – – – – x = –2 (vertical asymptote)
|
(–4,0) •————• (0,–6)
|
+————————→ x
The branch in x > –2 falls toward –∞ as x → –2⁺ and eventually levels off approaching y = –3 from below, while the branch in x < –2 comes from above (y → –3 from above as x → –∞) and falls to –∞ as x → –2⁻.
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(2) Equation of the vertical asymptote
Since the denominator vanishes when x + 2 = 0, the vertical asymptote is
x = –2.
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(3) Equation of the horizontal asymptote
As x → ±∞, the term –6/(x + 2) → 0. Hence, f(x) → –3. So the horizontal asymptote is
y = –3.
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(4) Domain of f
The function is undefined where the denominator is zero. So,
x + 2 ≠ 0 ⟹ x ≠ –2.
Thus, the domain is all real numbers except –2, i.e.,
{ x ∈ ℝ : x ≠ –2 } or (–∞, –2) ∪ (–2, ∞).
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(5) Range of f
Since f(x) is a transformed reciprocal function, its horizontal asymptote y = –3 is never reached. Therefore, the range is all real numbers except –3:
{ y ∈ ℝ : y ≠ –3 } or (–∞, –3) ∪ (–3, ∞).
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(6) Axes of symmetry of f
For a function to have an axis of symmetry, it must be mirror-reflective about a line (such as vertical or horizontal). In our case, let’s check:
Write x in terms relative to the vertical asymptote by letting t = x + 2 so that
f(x) = –6/t – 3.
Now consider f(–2 + t) and f(–2 – t):
f(–2 + t) = –6/t – 3,
f(–2 – t) = –6/(–t) – 3 = 6/t – 3.
These two are generally not equal (unless 6/t = –6/t, which happens only if 6/t = 0, an impossibility). Thus there is no vertical or horizontal line which is an axis of symmetry.
Note, however, that the graph has 180° rotational symmetry about the point where the asymptotes meet. That is, if you rotate the graph 180° around (–2, –3) you will get the same graph. However, this is point symmetry rather than symmetry with respect to an axis (i.e. a line of reflection).
Thus, the function has no axis of symmetry.
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Summary of Answers
1. The graph of f(x) = –6/(x + 2) – 3 is a hyperbola with a vertical asymptote at x = –2 and a horizontal asymptote at y = –3. It intercepts the y‑axis at (0, –6) and the x‑axis at (–4, 0), with one branch for x > –2 and the other for x < –2.
2. Vertical asymptote: x = –2.
3. Horizontal asymptote: y = –3.
4. Domain: { x ∈ ℝ : x ≠ –2 } or (–∞, –2) ∪ (–2, ∞).
5. Range: { y ∈ ℝ : y ≠ –3 } or (–∞, –3) ∪ (–3, ∞).
6. f has no axis of symmetry (though it is symmetric under a 180° rotation about the point (–2, –3)).
Any answer equivalent to the above is correct.
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