(Edited by Dionysius Lardner, 1855)

Proposition XLI. Theorem.

[Euclid, ed. Lardner, 1855, on `Google Books`]

(190) | If a parallelogram (B D) and a triangle (B E C) have the same base and be between the same parallels, the parallelogram is double of the triangle. |

Book I: Euclid, Book I (ed. Dionysius Lardner, 11th Edition, 1855)

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This proposition in other editions:

(191) This proposition may be generalized thus:

If a parallelogram and triangle have equal bases and altitudes, the parallelogram is double the triangle(175).(192) Also,

If a parallelogram and a triangle have equal altitudes, and the base of the triangle be double the base of the parallelogram, the parallelogram and triangle will be equal(178).(193)

If a parallelogram and triangle have equal bases, and the altitude of the triangle be double the altitude of the parallelogram, they will be equal.