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jmc

geometry senior

Problem

problem
Let be the set of points on the rays forming the sides of a angle, and let be a fixed point inside the angle on the angle bisector. Consider all distinct equilateral triangles with and in . (Points and may be on the same ray, and switching the names of and does not create a distinct triangle.) There are
problem
Points and are on a circle of diameter , and is on diameter If and , then
Solution
We have all the angles we need, but most obviously, we see that right angle in triangle . Note also that angle is 6 degrees, so length because the diameter, , is 1. Now, we can concentrate on triangle (after all, now we can decipher all angles easily and use Law of Sines). We get: That's equal to Therefore, our answer is equal to:
Final answer
\cos(6^\circ)\sin(12^\circ)\csc(18^\circ)