“ To continue, the proportion of the tangents of the angles opposite the vertical side are equivalent to the proportion of the sides that serve as secants. For example, as is the proportion of the tangent of angle ABC [to the tangent of angle ACD] so is the proportion of side DC to side BD. The proof to this is that the proportion of side CD to the maximum sine is equivalent to the proportion of side AD to the tangent of angle ABC, as was written in section 173. ”

“ Section 176 The third method: If the base line and the hypotenuse are known, for example lines AB and BC, then base can be set up in proportions in the same manner as was done with the vertical side in the previous section. ”