To solve the problem, we first need to clarify the functions \( f \) and \( g \). It seems there was a typo in your question, as you defined \( f(x) = 4x - 3 \) and \( a(x) = -9x^2 \), but then referred to \( g \) in the context of domains and operations. I will assume that \( g(x) = a(x) = -9x^2 \).
### Part a: Domains of \( \frac{f}{g} \) and \( \frac{g}{f} \)
1. **Domain of \( \frac{f}{g} \)**:
The function \( \frac{f}{g}(x) = \frac{4x - 3}{-9x^2} \) is undefined when \( g(x) = -9x^2 = 0 \). This occurs when \( x = 0 \). Therefore, the domain of \( \frac{f}{g} \) is:
\[
(-\infty, 0) \cup (0, \infty)
\]
2. **Domain of \( \frac{g}{f} \)**:
The function \( \frac{g}{f}(x) = \frac{-9x^2}{4x - 3} \) is undefined when \( f(x) = 4x - 3 = 0 \). This occurs when \( 4x = 3 \) or \( x = \frac{3}{4} \). Therefore, the domain of \( \frac{g}{f} \) is:
\[
\left(-\infty, \frac{3}{4}\right) \cup \left(\frac{3}{4}, \infty\right)
\]
### Part b: Simplifying \( (f + g)(x) \), \( (f - g)(x) \), and \( (fg)(x) \)
1. **Sum \( (f + g)(x) \)**:
\[
(f + g)(x) = f(x) + g(x) = (4x - 3) + (-9x^2) = -9x^2 + 4x - 3
\]
2. **Difference \( (f - g)(x) \)**:
\[
(f - g)(x) = f(x) - g(x) = (4x - 3) - (-9x^2) = 4x - 3 + 9x^2 = 9x^2 + 4x - 3
\]
3. **Product \( (fg)(x) \)**:
\[
(fg)(x) = f(x) \cdot g(x) = (4x - 3)(-9x^2)
\]
Expanding this:
\[
(fg)(x) = -9x^2(4x - 3) = -36x^3 + 27x^2
\]
### Final Answers
- The domain of \( \frac{f}{g} \) is \( (-\infty, 0) \cup (0, \infty) \).
- The domain of \( \frac{g}{f} \) is \( \left(-\infty, \frac{3}{4}\right) \cup \left(\frac{3}{4}, \infty\right) \).
- \( (f + g)(x) = -9x^2 + 4x - 3 \)
- \( (f - g)(x) = 9x^2 + 4x - 3 \)
- \( (fg)(x) = -36x^3 + 27x^2 \)
Domain of \( \frac{f}{g} \): \( (-\infty, 0) \cup (0, \infty) \)
Domain of \( \frac{g}{f} \): \( \left(-\infty, \frac{3}{4}\right) \cup \left(\frac{3}{4}, \infty\right) \)
\( (f + g)(x) = -9x^2 + 4x - 3 \)
\( (f - g)(x) = 9x^2 + 4x - 3 \)
\( (fg)(x) = -36x^3 + 27x^2 \)