Precalculus Quiz
1. **State the problem:** Determine the domain, range, and whether each given graph represents a function.
- **Top-left graph:** Vertical asymptote near $x=2$ and horizontal asymptote near $y=0$, branches in first and third quadrants (rational function).
- **Top-right graph:** Sinusoidal wave with multiple x-axis crossings (periodic sine or cosine function).
- **Bottom-left graph:** Piecewise linear "V" shape rising from bottom-left to top-right.
- **Bottom-right:** No graph.
**Step 1:** Identify domain for each graph:
- Top-left: All real numbers except where vertical asymptote occurs, so $\text{Domain} = (-\infty, 2) \cup (2, \infty)$.
- Top-right: Sinusoidal wave continuous for all real $x$, so $\text{Domain} = (-\infty, \infty)$.
- Bottom-left: Piecewise linear with no breaks, so $\text{Domain} = (-\infty, \infty)$.
**Step 2:** Identify range:
- Top-left: Horizontal asymptote $y=0$ approached but not crossed, branches in first and third quadrants mean range is $(-\infty, 0) \cup (0, \infty)$.
- Top-right: Sinusoidal wave oscillates between max and min, typically $[-1, 1]$ or similar; given no exact numbers, assume $\text{Range} = [-1,1]$.
- Bottom-left: V shape opens upward from bottom-left to top-right, minimum at vertex, so range starts at minimum value. Assuming vertex at origin: $\text{Range} = [0, \infty)$.
**Step 3:** Determine if each relation is a function:
- Top-left: Rational function with vertical asymptote, passes vertical line test, yes, function.
- Top-right: Sinusoidal wave, continuous function, yes.
- Bottom-left: V shape, piecewise linear, also function.
**Answers for item 1:**
- Top-left: Domain $(-\infty, 2) \cup (2, \infty)$; Range $(-\infty, 0) \cup (0, \infty)$; Function? Yes.
- Top-right: Domain $(-\infty, \infty)$; Range $[-1,1]$; Function? Yes.
- Bottom-left: Domain $(-\infty, \infty)$; Range $[0, \infty)$; Function? Yes.
2. **Find the value of $f(-7)$:**
No explicit function $f$ given in item 2, so unable to evaluate $f(-7)$. Possibly use in item 3.
3. **Evaluate $f(2x + 3)$ for $f(x) = -x^2 + 3x + 10$:**
Step 1: Substitute $x$ with $2x+3$ in the function:
$$f(2x+3) = -(2x+3)^2 + 3(2x+3) + 10$$
Step 2: Expand $(2x+3)^2$:
$$(2x+3)^2 = 4x^2 + 12x + 9$$
Step 3: Substitute and simplify:
$$f(2x+3) = -(4x^2 + 12x + 9) + 6x + 9 + 10$$
$$= -4x^2 - 12x - 9 + 6x + 9 + 10$$
Step 4: Combine like terms:
$$-4x^2 - 12x + 6x -9 + 9 + 10 = -4x^2 - 6x + 10$$
**Final answer for item 3:**
$$f(2x+3) = -4x^2 -6x + 10$$
4. **Find zero(s) and y-intercept for $f(x) = 4x^4 - 17x^2 + 4$:**
Step 1: Find zeros by solving $4x^4 - 17x^2 + 4 = 0$.
Step 2: Use substitution let $u = x^2$, then quadratic in $u$:
$$4u^2 - 17u + 4 = 0$$
Step 3: Solve quadratic using quadratic formula:
$$u = \frac{17 \pm \sqrt{(-17)^2 - 4 \times 4 \times 4}}{2 \times 4} = \frac{17 \pm \sqrt{289 - 64}}{8} = \frac{17 \pm \sqrt{225}}{8}$$
$$= \frac{17 \pm 15}{8}$$
Step 4: Calculate roots:
$$u_1 = \frac{17+15}{8} = \frac{32}{8} = 4$$
$$u_2 = \frac{17-15}{8} = \frac{2}{8} = \frac{1}{4}$$
Step 5: Back-substitute $u=x^2$:
$$x^2 = 4 \Rightarrow x = \pm 2$$
$$x^2 = \frac{1}{4} \Rightarrow x = \pm \frac{1}{2}$$
Step 6: Y-intercept is $f(0)$:
$$f(0) = 4(0)^4 - 17(0)^2 + 4 = 4$$
**Answer for item 4:**
Zero(s): $x = -2, -\frac{1}{2}, \frac{1}{2}, 2$; Y-intercept: $4$
5. **Find zero(s) and y-intercept for $f(x) = x^6 - 81x^4$:**
Step 1: Factor the function:
$$f(x) = x^4(x^2 - 81) = x^4(x - 9)(x + 9)$$
Step 2: Solve for zeros:
$$x^4 = 0 \Rightarrow x=0$$
$$x-9=0 \Rightarrow x=9$$
$$x+9=0 \Rightarrow x=-9$$
Step 3: Y-intercept is $f(0)$:
$$f(0) = 0 - 0 = 0$$
**Answer for item 5:** Zero(s): $x = -9, 0, 9$; Y-intercept: $0$