Circle...

Let 0 < a < b. Consider two circles with radii a and b and centers
(a, 0) and (b, 0) respectively with 0 < a < b. Let c be the center of any
circle in the crescent shaped region M between the two circles and
tangent to both (See figure below). Determine the locus of c as its
circle traverses through region M maintaining tangency.

2 Answers

383
Soumyabrata Mondal ·

This is the locus of an ellipse with foci at (a, 0) and (b, 0).

383
Soumyabrata Mondal ·

join ac & bc

if the radius of the small circle is r then
ac=a+r
bc=b-r

ac+bc= a+b (constant)

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