Many a mathematician has received a long letter from an unknown sender who claims to have found a way to trisect an angle using only a straightedge and compass. The mathematician may read passages of the letter aloud to the guffaws of colleagues at afternoon tea and then toss it out. Without even reading the details, any mathematician would know the writer is incorrect. In the early nineteenth century, the young French mathematician Évariste Galois proved the problem to be impossible.
More recently, mathematicians have found that it is possible to divide an angle into three equal parts by folding paper rather than using a straightedge and compass.