Piecewise Function
1. **State the problem:** We have the piecewise function
$$f(x)=\begin{cases}\sqrt{-x} & \text{if } x<0\\3 - x & \text{if } 0 \leq x < 3\\(x - 3)^2 & \text{if } x \geq 3\end{cases}$$
We want to:
(i) Find $\lim_{x\to 0} f(x)$ if it exists.
(ii) Show that $f(x)$ is continuous at $x=3$.
(iii) Sketch the graph of $f(x)$.
2. **Find $\lim_{x\to 0} f(x)$:**
- Left-hand limit as $x\to 0^-$: Since $x<0$, use $f(x) = \sqrt{-x}$.
$$\lim_{x \to 0^-} f(x) = \lim_{x \to 0^-} \sqrt{-x} = \sqrt{0} = 0.$$
- Right-hand limit as $x\to 0^+$: Since $0 \leq x < 3$, use $f(x) = 3-x$.
$$\lim_{x \to 0^+} f(x) = 3 - 0 = 3.$$
- Since $\lim_{x \to 0^-} f(x) = 0 \neq 3 = \lim_{x \to 0^+} f(x),$ the limit $\lim_{x \to 0} f(x)$ does not exist.
3. **Show continuity at $x=3$:**
- Compute $f(3)$ using the third case $f(x) = (x-3)^2$ for $x \geq 3$:
$$f(3) = (3 - 3)^2 = 0.$$
- Left-hand limit as $x \to 3^-$, use $f(x) = 3 - x$:
$$\lim_{x \to 3^-} f(x) = 3 - 3 = 0.$$
- Right-hand limit as $x \to 3^+$, use $f(x) = (x - 3)^2$:
$$\lim_{x \to 3^+} f(x) = (3 - 3)^2 = 0.$$
- Both limits and the function value at 3 are equal:
$$\lim_{x \to 3} f(x) = f(3) = 0,$$
so, $f$ is continuous at $x=3$.
4. **Sketch the graph:**
- For $x<0$, graph $y = \sqrt{-x}$, which is the square root reflected over the y-axis.
- For $0 \leq x < 3$, graph $y = 3 - x$, a line decreasing from 3 at $x=0$ to 0 at $x=3$.
- For $x \geq 3$, graph $y = (x - 3)^2$, a parabola starting at 0 at $x=3$ and opening upwards.
**Final answers:**
(i) $\lim_{x \to 0} f(x)$ does not exist.
(ii) $f$ is continuous at $x=3$.
(iii) The graph is as described above.