1. **State the problem:** Given the function $f(x) = (x - 2)(2x - 12)$, find the y-intercept, x-intercepts, line of symmetry, vertex, value at $x = -1$, and intervals where the function is increasing or decreasing.
2. **Expand the function:**
$$f(x) = (x - 2)(2x - 12) = 2x^2 - 12x - 4x + 24 = 2x^2 - 16x + 24$$
3. **Find the y-intercept:**
The y-intercept occurs when $x=0$.
$$f(0) = 2(0)^2 - 16(0) + 24 = 24$$
So, the y-intercept is $(0, 24)$.
4. **Find the x-intercepts:**
Set $f(x) = 0$:
$$(x - 2)(2x - 12) = 0$$
This gives two equations:
$$x - 2 = 0 \Rightarrow x = 2$$
$$2x - 12 = 0 \Rightarrow 2x = 12 \Rightarrow x = 6$$
So, the x-intercepts are $(2, 0)$ and $(6, 0)$.
5. **Equation for the line of symmetry:**
The line of symmetry for a quadratic $ax^2 + bx + c$ is given by:
$$x = -\frac{b}{2a}$$
Here, $a=2$, $b=-16$:
$$x = -\frac{-16}{2 \times 2} = \frac{16}{4} = 4$$
So, the line of symmetry is $x = 4$.
6. **Find the vertex:**
The vertex lies on the line of symmetry. Find $f(4)$:
$$f(4) = 2(4)^2 - 16(4) + 24 = 2(16) - 64 + 24 = 32 - 64 + 24 = -8$$
So, the vertex is at $(4, -8)$.
7. **Find $f(-1)$:**
$$f(-1) = 2(-1)^2 - 16(-1) + 24 = 2(1) + 16 + 24 = 42$$
8. **Determine intervals of increase and decrease:**
Since $a=2 > 0$, the parabola opens upward.
- It decreases on $(-\infty, 4)$
- It increases on $(4, \infty)$
**Final answers:**
- a) y-intercept: $(0, 24)$
- b) x-intercepts: $(2, 0)$ and $(6, 0)$
- c) Line of symmetry: $x = 4$
- d) Vertex: $(4, -8)$
- e) $f(-1) = 42$
- f) Increasing on $(4, \infty)$
- g) Decreasing on $(-\infty, 4)$
Quadratic Function Eedbb5
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