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Problem 485

AMC 12 late, AIME early

Geometry Difficulty 4.8 Find the answer

Ex. 2. Find the radius of the circle inscribed in a triangle with sides $9,10,11$ .

将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。

(Note: The note at the end is not part of the translation but is provided to clarify the instruction.)

Your answer

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Official solution

Ex. 2. $2 \sqrt{2}$ .

Source: NuminaMath-1.5, licensed Apache-2.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.