1. **State the problem:** Find the area under the curve of the function $f(x) = x^2 - 3x - 4$ where the graph is below the x-axis.
2. **Find the roots of the function:** Solve $x^2 - 3x - 4 = 0$ to find the points where the parabola intersects the x-axis.
Use the quadratic formula:
$$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
where $a=1$, $b=-3$, and $c=-4$.
Calculate the discriminant:
$$b^2 - 4ac = (-3)^2 - 4(1)(-4) = 9 + 16 = 25$$
Calculate the roots:
$$x = \frac{-(-3) \pm \sqrt{25}}{2(1)} = \frac{3 \pm 5}{2}$$
So,
$$x_1 = \frac{3 - 5}{2} = \frac{-2}{2} = -1$$
$$x_2 = \frac{3 + 5}{2} = \frac{8}{2} = 4$$
3. **Determine where the function is below the x-axis:** Since the parabola opens upward and roots are at $x=-1$ and $x=4$, the function is below the x-axis between $x=-1$ and $x=4$.
4. **Set up the integral for the area under the x-axis:**
The area under the x-axis is the integral of the negative of the function (to get positive area) from $x=-1$ to $x=4$:
$$\text{Area} = -\int_{-1}^{4} (x^2 - 3x - 4) \, dx$$
5. **Calculate the integral:**
Find the antiderivative:
$$\int (x^2 - 3x - 4) \, dx = \frac{x^3}{3} - \frac{3x^2}{2} - 4x + C$$
Evaluate from $-1$ to $4$:
$$\left[ \frac{x^3}{3} - \frac{3x^2}{2} - 4x \right]_{-1}^{4} = \left( \frac{4^3}{3} - \frac{3 \cdot 4^2}{2} - 4 \cdot 4 \right) - \left( \frac{(-1)^3}{3} - \frac{3 \cdot (-1)^2}{2} - 4 \cdot (-1) \right)$$
Calculate each part:
$$\frac{4^3}{3} = \frac{64}{3}$$
$$\frac{3 \cdot 4^2}{2} = \frac{3 \cdot 16}{2} = 24$$
$$4 \cdot 4 = 16$$
So the first part:
$$\frac{64}{3} - 24 - 16 = \frac{64}{3} - 40 = \frac{64 - 120}{3} = \frac{-56}{3}$$
Calculate the second part:
$$\frac{(-1)^3}{3} = \frac{-1}{3}$$
$$\frac{3 \cdot (-1)^2}{2} = \frac{3 \cdot 1}{2} = \frac{3}{2}$$
$$4 \cdot (-1) = -4$$
So the second part:
$$-\frac{1}{3} - \frac{3}{2} + 4 = -\frac{1}{3} - \frac{3}{2} + 4$$
Find common denominator 6:
$$-\frac{2}{6} - \frac{9}{6} + \frac{24}{6} = \frac{-2 - 9 + 24}{6} = \frac{13}{6}$$
6. **Subtract:**
$$\frac{-56}{3} - \frac{13}{6} = \frac{-112}{6} - \frac{13}{6} = \frac{-125}{6}$$
7. **Calculate the area:**
Since the integral is negative (area below x-axis), multiply by $-1$:
$$\text{Area} = - \left( \frac{-125}{6} \right) = \frac{125}{6} \approx 20.833$$
8. **Round to the nearest thousandth:**
$$20.833$$
**Final answer:**
$$\boxed{20.833}$$
Area Under X Axis C0Ffc0
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