1. **Problem statement:** We are given the quadratic function $$f(x) = -x^2 + 6x - 5$$ and need to analyze its graph and properties.
2. **Concavity:** The coefficient of $$x^2$$ is $$-1$$, which is negative, so the parabola opens downward (concave down).
3. **Vertex:** Use the vertex formula $$x = -\frac{b}{2a}$$ where $$a = -1$$ and $$b = 6$$.
$$x = -\frac{6}{2 \times (-1)} = -\frac{6}{-2} = 3$$
Find $$f(3)$$:
$$f(3) = -(3)^2 + 6(3) - 5 = -9 + 18 - 5 = 4$$
So the vertex is at $$(3, 4)$$.
4. **Axis of symmetry:** The vertical line through the vertex, $$x = 3$$.
5. **Y-intercept:** Set $$x=0$$:
$$f(0) = -0 + 0 - 5 = -5$$
So the y-intercept is $$(0, -5)$$.
6. **X-intercepts:** Solve $$f(x) = 0$$:
$$-x^2 + 6x - 5 = 0$$
Multiply both sides by $$-1$$ to simplify:
$$\cancel{-}x^2 + 6x - 5 = 0 \Rightarrow x^2 - 6x + 5 = 0$$
Factor or use quadratic formula:
$$x = \frac{6 \pm \sqrt{(-6)^2 - 4(1)(5)}}{2(1)} = \frac{6 \pm \sqrt{36 - 20}}{2} = \frac{6 \pm \sqrt{16}}{2}$$
$$x = \frac{6 \pm 4}{2}$$
So,
$$x = \frac{6 + 4}{2} = 5$$ and $$x = \frac{6 - 4}{2} = 1$$
X-intercepts are $$(1, 0)$$ and $$(5, 0)$$.
7. **Domain:** Quadratic functions have domain all real numbers:
$$\text{Domain} = (-\infty, \infty)$$
8. **Range:** Since the parabola opens downward and vertex is maximum at $$y=4$$,
$$\text{Range} = (-\infty, 4]$$
9. **Increasing and decreasing intervals:**
- The function increases on the interval to the left of the vertex: $$(-\infty, 3)$$
- The function decreases on the interval to the right of the vertex: $$(3, \infty)$$
10. **Where $$f(x) > 0$$ and $$f(x) < 0$$:**
- $$f(x) > 0$$ between the x-intercepts: $$(1, 5)$$
- $$f(x) < 0$$ outside the x-intercepts: $$(-\infty, 1) \cup (5, \infty)$$
**Summary:**
- Concave down
- Vertex at $$(3,4)$$
- Axis of symmetry $$x=3$$
- Y-intercept $$(0,-5)$$
- X-intercepts $$(1,0)$$ and $$(5,0)$$
- Domain $$(-\infty, \infty)$$
- Range $$(-\infty, 4]$$
- Increasing on $$(-\infty, 3)$$
- Decreasing on $$(3, \infty)$$
- $$f(x) > 0$$ on $$(1, 5)$$
- $$f(x) < 0$$ on $$(-\infty, 1) \cup (5, \infty)$$
Quadratic Analysis 60Ab99
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