2018 AIME I Problems/Problem 8
Contents
Problem
Let be an equiangular hexagon such that , and . Denote by the diameter of the largest circle that fits inside the hexagon. Find .
Solution 1
- cooljoseph
First of all, draw a good diagram! This is always the key to solving any geometry problem. Once you draw it, realize that . Why? Because since the hexagon is equiangular, we can put an equilateral triangle around it, with side length . Then, if you drew it to scale, notice that the "widest" this circle can be according to is . And it will be obvious that the sides won't be inside the circle, so our answer is .
-expiLnCalc
Solution 2
Like solution 1, draw out the large equilateral triangle with side length . Let the tangent point of the circle at be G and the tangent point of the circle at be H. Clearly, GH is the diameter of our circle, and is also perpendicular to and .
The equilateral triangle of side length is similar to our large equilateral triangle of . And the height of the former equilateral triangle is . By our similarity condition,
Solving this equation gives , and
~novus677
Note:
This is because the altitude of our equilateral triangle with side length is perpendicular to the tangent line to the circle, which implies they are all degrees (two degree angles from altitude, two degree angles from tangent lines). This allows us to calculate further. Tilt your head degrees clockwise if you can't see what is being done. ~IronicNinja
See Also
2018 AIME I (Problems • Answer Key • Resources) | ||
Preceded by Problem 7 |
Followed by Problem 9 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
All AIME Problems and Solutions |
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