A Parallelepipedon is divided into Two equally, by a Diagonal Plane.
Let the Parallelepipedon AB be divi∣ded
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A Parallelepipedon is divided into Two equally, by a Diagonal Plane.
Let the Parallelepipedon AB be divi∣ded
by the Plane CD, drawn from one Angle to the other: I say that it divideth the same into Two equally Let the Line EA, be supposed to be divided into as many parts as one listeth; and that from each, one hath drawn as many Planes parallel to the Base AF; each of those Planes is a Parallelogram equal to the Base AF (by the 24th.)
Demonstration. All the Parallelograms which can be drawn parallel to the Base AF, are divided into Two equally by the Plane CD; for the Triangle which will be made on each side of the Plane CD, have their common Base equal to CG; and their sides equal, seeing they are those of a parallelogram. Now it is evident that the Parallelepipedon AB, containeth nothing else but its parallelo∣gram Surfaces, each of which is divided into Two equal Triangles: therefore the parallelepipedon AB, is divided into Two equally by the Plane CD.
The Twenty Seventh and Twenty Eighth Propopositions are useless, according to this way of Demonstration.