Function Evaluation
1. **State the problem:** We have three functions:
- $f(x)=\frac{4x+5}{1-2x}$
- $g(x)=3x+5$
- $h(x)=px^2+q-1$
We need to find values and expressions as per the sub-questions.
2. **(a)(i) Find $f\left(-\frac{1}{2}\right)$:**
$$f\left(-\frac{1}{2}\right)=\frac{4\left(-\frac{1}{2}\right)+5}{1-2\left(-\frac{1}{2}\right)}=\frac{-2+5}{1+1}=\frac{3}{2}$$
3. **(a)(ii) Find $g(-2)$:**
$$g(-2)=3(-2)+5=-6+5=-1$$
4. **(a)(iii) Find $q$ given $h(0)=-4$:**
Substitute $x=0$ into $h(x)$:
$$h(0)=p(0)^2+q-1=q-1=-4$$
Solve for $q$:
$$q-1=-4 \implies q=-3$$
5. **(a)(iv) Find $x$ making $f$ undefined:**
$f$ is undefined when the denominator is zero:
$$1-2x=0 \implies x=\frac{1}{2}$$
6. **(b)(i) Find $f^{-1}(x)$ (inverse of $f$):**
Start with $y=\frac{4x+5}{1-2x}$ and solve for $x$ in terms of $y$.
$$y=\frac{4x+5}{1-2x} \implies y(1-2x)=4x+5$$
$$y - 2xy = 4x + 5$$
Group $x$ terms:
$$y - 5 = 4x + 2xy = x(4+2y)$$
Solve for $x$:
$$x=\frac{y-5}{4+2y}$$
Thus,
$$f^{-1}(x)=\frac{x-5}{4+2x}$$
7. **(b)(ii) Find $(fg)(x) = f(g(x))$:**
Substitute $g(x)$ into $f$:
$$f(g(x))=f(3x+5) = \frac{4(3x+5)+5}{1-2(3x+5)} = \frac{12x+20+5}{1 - 6x - 10} = \frac{12x+25}{-6x - 9}$$
Simplify denominator:
$$-6x -9 = -3(2x +3)$$
So,
$$(fg)(x) = \frac{12x+25}{-6x - 9}$$
8. **(c) Find $x$ such that $f^{-1}(x) = -1$:**
Substitute and solve:
$$-1 = \frac{x-5}{4 + 2x}$$
Multiply both sides:
$$-1(4 + 2x) = x - 5$$
$$-4 - 2x = x - 5$$
$$-4 + 5 = x + 2x$$
$$1 = 3x \implies x = \frac{1}{3}$$
**Final answers:**
- $f\left(-\frac{1}{2}\right) = \frac{3}{2}$
- $g(-2) = -1$
- $q = -3$
- $f$ undefined at $x=\frac{1}{2}$
- $f^{-1}(x) = \frac{x-5}{4+2x}$
- $(fg)(x) = \frac{12x+25}{-6x - 9}$
- $f^{-1}(x) = -1$ when $x=\frac{1}{3}$