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jmc

geometry senior

Problem

In the configuration below, is measured in radians, is the center of the circle, and are line segments and is tangent to the circle at .
problem
A necessary and sufficient condition for the equality of the two shaded areas, given , is
Solution
Well, the shaded sector's area is basically . In addition, if you let , thenThen the area of that shaded thing on the left becomesWe want this to be equal to the sector area so
Final answer
\tan \theta = 2\theta