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 ...

Without changing the distance between the pencil and compass point, place your compass at the other end of the line and draw another arc - crossing the first arc in two places.

The second is an Angle, Side, Angle (ASA) construction where two angles and the side between them is known. To construct an SAS triangle: Draw the longest given side of the triangle using a ruler.