Domain Range Inverses
1. Define the concepts:
(i) Domain is the set of all possible input values (x-values) for which the function is defined.
(ii) Range is the set of all possible output values (y-values) that the function can take.
2. Find domain and range:
(i) For $y=24+10x-x^2$:
- This is a quadratic function (a parabola) opening downward because the coefficient of $x^2$ is negative.
- Domain: All real numbers, $\mathbf{\mathbb{R}}$, since any $x$ can be plugged in.
- Range: Maximum value at vertex. The vertex $x$-coordinate is $x=-\frac{b}{2a}=-\frac{10}{2(-1)}=5$.
- Substitute $x=5$ into $y$: $$y=24+10(5)-5^2=24+50-25=49$$
- So, range is $(-\infty, 49]$.
(ii) For $y=\frac{1}{6\sqrt{x^2}}$:
- $\sqrt{x^2}=|x|$.
- Function becomes $y=\frac{1}{6|x|}$.
- Domain: $x\neq 0$ because denominator can't be zero.
- Range: Since $|x|>0$, $y>0$ and as $|x|\to \infty$, $y\to 0^{+}$.
- So, range is $(0, \infty)$.
3. Find inverse functions:
(i) For $f:x\to \frac{x+1}{x+2}$:
- Set $y=\frac{x+1}{x+2}$.
- Solve for $x$: $$y(x+2) = x+1 \Rightarrow yx + 2y = x+1 \Rightarrow yx - x = 1 - 2y \Rightarrow x(y-1) = 1-2y \Rightarrow x = \frac{1-2y}{y-1}$$
- Thus, inverse $f^{-1}: y \to \frac{1-2y}{y-1}$.
(ii) For $g:y \to 3y + 2$:
- Set $z=3y+2$.
- Solve for $y$: $$3y = z-2 \Rightarrow y=\frac{z-2}{3}$$
- Thus, inverse $g^{-1}: z \to \frac{z-2}{3}$.
(iii) Find $f^{-1}(g^{-1}(2))$:
- Compute $g^{-1}(2)$: $$g^{-1}(2) = \frac{2-2}{3} = 0$$
- Compute $f^{-1}(0)$: $$f^{-1}(0) = \frac{1-2(0)}{0-1} = \frac{1}{-1} = -1$$
Final answers:
(i) Domain and Range:
- $y=24+10x-x^2$ domain: $\mathbf{\mathbb{R}}$, range: $(-\infty, 49]$.
- $y=\frac{1}{6\sqrt{x^2}}$ domain: $\mathbf{\mathbb{R}} \setminus \{0\}$, range: $(0, \infty)$.
(ii) Inverses:
- $f^{-1}: y \to \frac{1-2y}{y-1}$.
- $g^{-1}: z \to \frac{z-2}{3}$.
(iii) $f^{-1}(g^{-1}(2)) = -1$.