1. **Problem Statement:**
We are given the function $$y = x(x - 4) - 5$$ which simplifies to $$y = x^2 - 4x - 5$$.
We need to draw its graph for $$-3 \leq x \leq 4$$ and use it to solve the following equations:
a) $$x^2 - 5x - 3 = 0$$
b) $$x^2 - 3x - 4 = 0$$
2. **Graphing the function:**
The function is a quadratic polynomial, a parabola opening upwards because the coefficient of $$x^2$$ is positive.
The vertex formula for a parabola $$y = ax^2 + bx + c$$ is at $$x = -\frac{b}{2a}$$.
Here, $$a = 1$$ and $$b = -4$$, so
$$x = -\frac{-4}{2 \times 1} = \frac{4}{2} = 2$$.
The vertex point is at $$x=2$$.
Calculate $$y$$ at $$x=2$$:
$$y = 2^2 - 4 \times 2 - 5 = 4 - 8 - 5 = -9$$.
So the vertex is at $$(2, -9)$$.
3. **Using the graph to solve the equations:**
We want to find the roots of the given equations by comparing them to the graph of $$y = x^2 - 4x - 5$$.
Rewrite each equation in the form $$y = 0$$:
For a) $$x^2 - 5x - 3 = 0$$
For b) $$x^2 - 3x - 4 = 0$$
4. **Relate each equation to the graph:**
Note that the graph is $$y = x^2 - 4x - 5$$.
We can write each equation as:
For a): $$x^2 - 5x - 3 = 0$$
Rewrite as $$x^2 - 4x - 5 = (x^2 - 5x - 3) + (x - 2)$$
So,
$$y = x^2 - 4x - 5 = (x^2 - 5x - 3) + (x - 2)$$
Set $$y = 0$$ to find roots of the original equation:
$$0 = (x^2 - 5x - 3) + (x - 2)$$
This means the roots of $$x^2 - 5x - 3 = 0$$ are where the graph $$y = x^2 - 4x - 5$$ intersects the line $$y = -(x - 2)$$.
Similarly for b):
$$x^2 - 3x - 4 = 0$$
Rewrite as
$$x^2 - 4x - 5 = (x^2 - 3x - 4) - (x + 1)$$
Set $$y = 0$$:
$$0 = (x^2 - 3x - 4) - (x + 1)$$
So roots of $$x^2 - 3x - 4 = 0$$ are where the graph $$y = x^2 - 4x - 5$$ intersects the line $$y = x + 1$$.
5. **Solve each quadratic directly (for exact roots):**
For a) $$x^2 - 5x - 3 = 0$$
Use quadratic formula:
$$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} = \frac{5 \pm \sqrt{25 + 12}}{2} = \frac{5 \pm \sqrt{37}}{2}$$
Approximate roots:
$$x \approx \frac{5 + 6.08}{2} = 5.54$$ (outside domain) and $$x \approx \frac{5 - 6.08}{2} = -0.54$$ (inside domain).
For b) $$x^2 - 3x - 4 = 0$$
Quadratic formula:
$$x = \frac{3 \pm \sqrt{9 + 16}}{2} = \frac{3 \pm 5}{2}$$
Roots:
$$x = 4$$ and $$x = -1$$ (both inside domain).
6. **Summary:**
- The graph of $$y = x^2 - 4x - 5$$ is a parabola with vertex at $$(2, -9)$$.
- Equation a) has one root in the domain at approximately $$x = -0.54$$.
- Equation b) has two roots in the domain at $$x = -1$$ and $$x = 4$$.
These roots correspond to the points where the graph intersects the x-axis for the respective equations.
Quadratic Graph C0584A
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