Common Region Area
1. **State the problem:** Find the area of the common region bounded by the circle $$(x-2)^2+(y-2)^2=4$$, the line $$x+y=2$$, and the ellipse $$\frac{x^2}{9}+\frac{y^2}{4}=1$$.
2. **Analyze each curve:**
- Circle: center at $(2,2)$ with radius $2$.
- Line: rearranged as $$y=2-x$$.
- Ellipse: centered at origin with semi-major axis $3$ (along x-axis) and semi-minor axis $2$ (along y-axis).
3. **Find intersection points:**
- Between circle and line:
Substitute $$y=2-x$$ into circle:
$$ (x-2)^2 + (2 - x - 2)^2 = 4 $$
$$ (x-2)^2 + (-x)^2 = 4 $$
$$ (x-2)^2 + x^2 = 4 $$
$$ x^2 - 4x + 4 + x^2 = 4 $$
$$ 2x^2 - 4x + 4 = 4 $$
$$ 2x^2 - 4x = 0 $$
$$ 2x(x - 2) = 0 $$
So, $$x=0$$ or $$x=2$$.
For $$x=0$$, $$y=2-0=2$$.
For $$x=2$$, $$y=2-2=0$$.
Intersection points: $(0,2)$ and $(2,0)$.
- Between circle and ellipse:
Substitute $$y$$ from circle into ellipse or vice versa is complicated; instead, check if points $(0,2)$ and $(2,0)$ lie on ellipse:
For $(0,2)$:
$$\frac{0^2}{9} + \frac{2^2}{4} = 0 + 1 = 1$$, lies on ellipse.
For $(2,0)$:
$$\frac{2^2}{9} + \frac{0^2}{4} = \frac{4}{9} + 0 = \frac{4}{9} < 1$$, inside ellipse.
- Between line and ellipse:
Substitute $$y=2-x$$ into ellipse:
$$\frac{x^2}{9} + \frac{(2-x)^2}{4} = 1$$
Multiply both sides by 36 (LCM of 9 and 4):
$$4x^2 + 9(2 - x)^2 = 36$$
$$4x^2 + 9(4 - 4x + x^2) = 36$$
$$4x^2 + 36 - 36x + 9x^2 = 36$$
$$13x^2 - 36x + 36 = 36$$
$$13x^2 - 36x = 0$$
$$x(13x - 36) = 0$$
$$x=0$$ or $$x=\frac{36}{13} \approx 2.77$$
For $$x=0$$, $$y=2$$ (point $(0,2)$ already found).
For $$x=2.77$$, $$y=2-2.77 = -0.77$$.
4. **Determine the common region:**
- The common region is bounded by the circle, line, and ellipse, intersecting at points $(0,2)$ and $(2,0)$.
5. **Set up integral for area:**
- The area is the integral over $$x$$ from 0 to 2 of the minimum of the upper boundaries minus the maximum of the lower boundaries.
- Upper boundary is the circle or ellipse, lower boundary is the line.
6. **Express $$y$$ from circle:**
$$ (x-2)^2 + (y-2)^2 = 4 $$
$$ (y-2)^2 = 4 - (x-2)^2 $$
$$ y-2 = \pm \sqrt{4 - (x-2)^2} $$
Upper semicircle: $$ y = 2 + \sqrt{4 - (x-2)^2} $$
Lower semicircle: $$ y = 2 - \sqrt{4 - (x-2)^2} $$
7. **Express $$y$$ from ellipse:**
$$ \frac{x^2}{9} + \frac{y^2}{4} = 1 $$
$$ y^2 = 4(1 - \frac{x^2}{9}) = 4 - \frac{4x^2}{9} $$
$$ y = \pm \sqrt{4 - \frac{4x^2}{9}} = \pm \frac{2}{3} \sqrt{9 - x^2} $$
8. **Determine which curve is upper between 0 and 2:**
- At $$x=1$$:
Circle upper: $$2 + \sqrt{4 - (1-2)^2} = 2 + \sqrt{4 - 1} = 2 + \sqrt{3} \approx 3.732$$
Ellipse upper: $$\frac{2}{3} \sqrt{9 - 1} = \frac{2}{3} \sqrt{8} \approx 1.885$$
So circle upper is above ellipse upper.
9. **Line $$y=2-x$$ is below both curves between 0 and 2.**
10. **Area of common region:**
- The region bounded by line, circle, and ellipse between $$x=0$$ and $$x=2$$ is the area under the circle upper curve minus the area under the line, but also bounded by the ellipse.
- Since ellipse is inside circle in this interval, the common region is bounded by line, ellipse, and circle.
11. **Calculate area between line and ellipse from $$x=0$$ to $$x=2$$:**
$$ A_1 = \int_0^2 \left( \frac{2}{3} \sqrt{9 - x^2} - (2 - x) \right) dx $$
12. **Calculate area between circle and ellipse from $$x=0$$ to $$x=2$$:**
$$ A_2 = \int_0^2 \left( 2 + \sqrt{4 - (x-2)^2} - \frac{2}{3} \sqrt{9 - x^2} \right) dx $$
13. **Total common area:**
$$ A = A_1 + A_2 = \int_0^2 \left( 2 + \sqrt{4 - (x-2)^2} - (2 - x) \right) dx $$
14. **Simplify integrand:**
$$ 2 + \sqrt{4 - (x-2)^2} - 2 + x = x + \sqrt{4 - (x-2)^2} $$
15. **Final integral:**
$$ A = \int_0^2 \left( x + \sqrt{4 - (x-2)^2} \right) dx $$
16. **Evaluate integral:**
- Split integral:
$$ \int_0^2 x dx + \int_0^2 \sqrt{4 - (x-2)^2} dx $$
- First integral:
$$ \int_0^2 x dx = \left[ \frac{x^2}{2} \right]_0^2 = 2 $$
- Second integral is area under semicircle of radius 2 centered at 2:
Substitute $$u = x - 2$$, when $$x=0, u=-2$$; when $$x=2, u=0$$
$$ \int_0^2 \sqrt{4 - (x-2)^2} dx = \int_{-2}^0 \sqrt{4 - u^2} du $$
- Area of semicircle from $$-2$$ to $$0$$ is quarter circle area:
$$ \int_{-2}^0 \sqrt{4 - u^2} du = \frac{\pi \times 2^2}{4} = \pi $$
17. **Sum results:**
$$ A = 2 + \pi $$
**Answer:** The area of the common region is $$2 + \pi$$ square units.