The figure below shows a right triangle ABC (angle B = 90 degree)
with the incircle I tangent to AB and AC at D and G, respectively. The excircle E corresponding to BC is
tangent to BC at F. Prove that the
measure of the angle FDG is 45 degree.

See also: Typography and poster of problem 1408.

Geometry Problems

Ten problems: 1411-1420

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Triangle

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Excircle

Tangent Line

Perpendicular lines

45 degrees

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