The Pamphlet Collection of Sir Robert Stout: Volume 78
Areas
Areas.
Parallelograms on the same or equal bases and of the same altitude are equal in area.
Triangles on the same or equal bases and of the same altitude are equal in area.
Equal triangles on the same or equal bases are of the same altitude.
page 18Illustrations and explanations of the geometrical theorems corresponding to the following algebraical identities (these are necessarily omitted).