Three Greek problems of antiquity
The three Greek problems of antiquity were some of the most famous unsolved problems in history. They were first posed by the Greeks but were not settled till the advent of Abstract algebra and Analysis in modern times.
All three constructions have been shown to be impossible.
Trisection of the General Angle
Statement: Given an angle, construct by means of straight edge and compass only, an angle one-third its measure. This is impossible because the non-algebraic number would have to be constructable in this case.
Doubling of a Cube
Given a cube, construct by means of straight edge and compass only, a cube with double the volume. This is impossible, because the number would have to be constructed, and constructions can only construct square roots and arithmetic operations.
Squaring of a Circle
This was shown to be impossible, as the transcendental number would have to be constructable in this case.