Euclid
Father of geometry, wrote Elements
Quotes by Euclid
If a straight line falling on two straight lines make the alternate angles equal to one another, the straight lines will be parallel to one another.
If a straight line falling on two straight lines make the exterior angle equal to the interior and opposite angle on the same side, or the interior angles on the same side equal to two right angles, the straight lines will be parallel to one another.
A straight line falling on parallel straight lines makes the alternate angles equal to one another, the exterior angle equal to the interior and opposite angle, and the interior angles on the same side equal to two right angles.
Straight lines which are parallel to the same straight line are also parallel to one another.
Through a given point to draw a straight line parallel to a given straight line.
In any triangle, if one of the sides be produced, the exterior angle is equal to the two interior and opposite angles, and the three interior angles of the triangle are equal to two right angles.
Straight lines joining equal and parallel straight lines towards the same parts are themselves equal and parallel.
In parallelogrammic areas the opposite sides and angles are equal to one another, and the diameter bisects them.
Parallelograms which are on the same base and in the same parallels are equal to one another.
Parallelograms which are on equal bases and in the same parallels are equal to one another.
Triangles which are on the same base and in the same parallels are equal to one another.
Triangles which are on equal bases and in the same parallels are equal to one another.
Equal triangles which are on the same base and on the same side of it are also in the same parallels.
Equal triangles which are on equal bases and on the same side of them are also in the same parallels.
If a parallelogram have the same base with a triangle and be in the same parallels, the parallelogram is double of the triangle.
To construct a parallelogram equal to a given triangle in a given rectilineal angle.
In any parallelogram the complements of the parallelograms about the diameter are equal to one another.
To a given straight line to apply, in a given rectilineal angle, a parallelogram equal to a given triangle.
To construct a parallelogram equal to a given rectilineal figure in a given rectilineal angle.
On a given straight line to describe a square.