The Elements

Equal to the
to the a and to the
k straight line?

The remaining angle bal angle? is equal to [angle] dba. Let the abg be added to the common straight line. Therefore, the [angles] bad and bag are equal to the [angles] db and babg; for they were shown [to be] equal. Showing [that] the be straight lines [are] equal to the same, [and] equal to the same [things] to each other; and the [angles] beb and bel, but the [angles] dba and babg are equal to the [angles] be, dbg; for they are equal dba and babg; the remaining angles [are] equal, which the bae g tangents?... and the right angles? ... ...?

A small geometric diagram on the right margin consists of a horizontal line with an oblique line segment intersecting it to form an acute and obtuse angle.

A small geometric diagram on the left margin, positioned slightly lower than the one on the right, showing a similar arrangement of intersecting lines forming angles.

if ... ...? of it ... ...?
the [things] ... ...? ... ...?
... ... ...? ...
... ... ...? ...

?
... ... ...
... ... ...
... ... ...
... ... ...
... ... ...
... ... ...

A small geometric angle diagram in the upper right margin, consistent with the diagrams on the preceding page.

A large, complex geometric diagram at the bottom of the page features several intersecting lines that form triangles and possibly indicate projections or more advanced Euclidean proofs.