Question: 5. Rational Function Construction
Design a rational function that has:
(a)
i. Vertical asymptotes at x = -3 and x = 1.
ii. A hole at x = -2.
(b) i. x-intercepts at x = 4 and x = 0.
ii. Horizontal asymptote at y = 2.
(c)
i. Find the specific rational function.
ii. Verify that all conditions are satisfied.
1. **State the problem:**
We need to construct a rational function $f(x) = \frac{P(x)}{Q(x)}$ that satisfies:
- Vertical asymptotes at $x = -3$ and $x = 1$.
- A hole at $x = -2$.
- x-intercepts at $x = 4$ and $x = 0$.
- Horizontal asymptote at $y = 2$.
2. **Recall formulas and rules:**
- Vertical asymptotes occur where the denominator is zero but the numerator is not zero.
- Holes occur where both numerator and denominator are zero at the same $x$ value.
- x-intercepts occur where the numerator is zero but the denominator is not zero.
- Horizontal asymptote depends on degrees of numerator and denominator:
- If degrees are equal, horizontal asymptote is ratio of leading coefficients.
3. **Construct denominator $Q(x)$:**
- Vertical asymptotes at $x = -3$ and $x = 1$ imply factors $(x + 3)$ and $(x - 1)$ in denominator.
- Hole at $x = -2$ implies factor $(x + 2)$ in denominator and numerator.
So,
$$Q(x) = (x + 3)(x - 1)(x + 2)$$
4. **Construct numerator $P(x)$:**
- Hole at $x = -2$ means numerator also has factor $(x + 2)$.
- x-intercepts at $x = 4$ and $x = 0$ imply factors $(x - 4)$ and $x$ in numerator.
So,
$$P(x) = k \cdot x (x - 4)(x + 2)$$
where $k$ is a constant to be determined.
5. **Determine $k$ using horizontal asymptote:**
- Degree numerator = degree denominator = 3.
- Horizontal asymptote $y = 2$ means leading coefficient ratio = 2.
Leading coefficient numerator: $k \cdot 1 \cdot 1 \cdot 1 = k$
Leading coefficient denominator: $1 \cdot 1 \cdot 1 = 1$
So,
$$\frac{k}{1} = 2 \implies k = 2$$
6. **Final function:**
$$f(x) = \frac{2x(x - 4)(x + 2)}{(x + 3)(x - 1)(x + 2)}$$
7. **Simplify by canceling hole factor:**
$$f(x) = \frac{\cancel{(x + 2)} 2x (x - 4)}{(x + 3)(x - 1) \cancel{(x + 2)}} = \frac{2x(x - 4)}{(x + 3)(x - 1)}$$
8. **Verify conditions:**
- Vertical asymptotes at $x = -3$ and $x = 1$ because denominator zero and numerator nonzero.
- Hole at $x = -2$ because factor canceled.
- x-intercepts at $x = 0$ and $x = 4$ because numerator zero and denominator nonzero.
- Horizontal asymptote $y = 2$ because degrees equal and leading coefficient ratio is 2.
**Answer:**
$$\boxed{f(x) = \frac{2x(x - 4)}{(x + 3)(x - 1)}}$$