Proposition 35
Theorem
Two parallelograms (◇ABCD , ◇BCEF ) on the same base (BC ) and between the same parallels (BC ‖ AE ) have the same area.
τὰ παραλληλόγραμμα τὰ ἐπὶ τῆς αὐτῆς βάσϵως ὄντα καὶ ἐν ταῖς αὐταῖς παραλλήλοις ἴσα ἀλλήλοις ἐστίν.
Parallelograms which are on the same base and in the same parallels are equal to one another.