Let be the region in the Cartesian plane of points satisfying , and . Determine the area of .
Solution
We claim that a point in the first quadrant satisfies the desired property if the point is below the line and does not satisfy the desired property if it is above the line. To see this, for a point inside the region, and However, must equal to an integer. Thus, . Adding these two equations, , which satisfies the desired property. Conversely, for a point outside the region, However, . Thus, , so , implying that . To finish, is the region bounded by the x -axis, the y -axis, and the line is a right triangle whose legs have length 3. Consequently, has area .
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