Do you have a specific problem?
All right, why don't I just give you the whole thing.
30 knights sit at King Arthur's round table. The table has a radius of 12 ft. Each knight has a lance that is 10 ft long. As King Arthur walks by each knight raises his lance and taps the lance of those it can reach. How many neighboring lances can one knight touch?
The student that asked this problem (elsewhere) is in 9th grade doing Geometry, and thus cannot use Trigonometry. I'm stumped!
I think the only way to solve the problem without using trigonometry is to draw a diagram. What you do is draw a circle of radius 12, mark 30 equally spaced points on the circumference, then draw a circle of radius 20 with any one of these points as centre. (Each knight can touch the lance of another knight up to 20 ft away if both knights use their lances.) Then you just count how many points are contained in the second circle. (I think the answer is 18.)
It seems to me that in order to be able to find the length that number (the length) needs to be a constructible number if you are only using geometry without triginometry. But that would mean some are impossible to construct for not all real numbers are constructible (for instance all real algebraic numbers of degree 3 over Q are not constructible). I am really not sure about this but the reasoning seems to work.