What is the area of the region in the complex plane consisting of all points satisfying both and ? ( denotes the magnitude of a complex number, i.e. .)
Problem 1333
Official solution
1. Interpret the inequalities geometrically:
- The inequality describes the interior of a unit circle centered at in the complex plane.
- The inequality can be rewritten by clearing the denominator. Let where and are real numbers.
2. Rewrite the first inequality:
This inequality is satisfied by all with real part . This can be shown by considering the geometric interpretation of the magnitudes.
3. Combine the regions:
- The region is a unit circle centered at .
- The region is the half-plane where the real part of is greater than .
4. Find the intersection:
- The intersection of these two regions is the part of the unit circle centered at that lies to the right of the vertical line .
5. Calculate the area:
- The intersection forms a sector of the circle and a triangle.
- The angle of the sector is radians (since the line intersects the circle at angles from the positive real axis).
- The area of the sector is:
- The area of the triangle formed by the intersection points and the center of the circle is:
6. Sum the areas:
The final answer is