Problem:
A circle is tangent to both branches of the hyperbola as well as the -axis. Compute the area of this circle.
, 2024
Solutions — 2
Solution 1
Solution:
Invert about the unit circle centered at the origin. turns into a horizontal line, and the hyperbola turns into the following:
This means that the horizontal line in question is . This means that the diameter of the circle is the reciprocal of the distance between the point and line, which is , so the radius is , and the answer is .
Solution 2
Solution:
Let be the -coordinate of both tangency points to the hyperbola. Then, the equation of the circle must be in the form
Comparing the -coefficient, we see that . Moreover, we need it to pass through , so . Thus, the equation of the circle is
so the radius is , and the area is .
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