Area Under Curve
1. **State the problem:** We have the function $$y = -(x-3)(x+1)$$ and a table with values of $$x$$ and corresponding $$y$$ values. We need to fill in the missing values (Box 1, Box 2, Box 3) for $$x=0,1,2$$.
2. **Calculate the missing values:**
- For $$x=0$$: $$y = -(0-3)(0+1) = -(-3)(1) = 3$$ (Box 1 = 3)
- For $$x=1$$: $$y = -(1-3)(1+1) = -(-2)(2) = 4$$ (Box 2 = 4)
- For $$x=2$$: $$y = -(2-3)(2+1) = -(-1)(3) = 3$$ (Box 3 = 3)
3. **Use the trapezium rule to approximate the area of region R between $$x=0$$ and $$x=3$$:**
The trapezium rule formula for interval $$[a,b]$$ with equal subintervals of width $$h$$ is:
$$\text{Area} \approx \frac{h}{2} \left(y_0 + 2y_1 + 2y_2 + \cdots + 2y_{n-1} + y_n\right)$$
Here, $$a=0$$, $$b=3$$, and the points are at $$x=0,1,2,3$$ with $$y$$ values $$3,4,3,0$$ respectively.
- Number of subintervals $$n=3$$
- Width $$h = \frac{3-0}{3} = 1$$
Calculate:
$$\text{Area} \approx \frac{1}{2} (3 + 2\times4 + 2\times3 + 0) = \frac{1}{2} (3 + 8 + 6 + 0) = \frac{1}{2} (17) = 8.5$$
4. **Calculate the exact area by integration:**
The area $$A$$ is the integral of $$y$$ from $$x=0$$ to $$x=3$$:
$$A = \int_0^3 -(x-3)(x+1) \, dx$$
Expand the integrand:
$$-(x-3)(x+1) = -(x^2 + x - 3x - 3) = -(x^2 - 2x - 3) = -x^2 + 2x + 3$$
Integrate term-by-term:
$$\int_0^3 (-x^2 + 2x + 3) \, dx = \left[-\frac{x^3}{3} + x^2 + 3x \right]_0^3$$
Evaluate at $$x=3$$:
$$-\frac{27}{3} + 9 + 9 = -9 + 9 + 9 = 9$$
Evaluate at $$x=0$$:
$$0$$
So,
$$A = 9 - 0 = 9$$
**Final answers:**
- Box 1 = 3
- Box 2 = 4
- Box 3 = 3
- Approximate area using trapezium rule = 8.5
- Exact area by integration = 9