The ratios of rectilinear figures form the same field Q as the ratios of lines. This follows from the theory of application of areas developed in Book I, see proposition I.44 . The ratio of a circle to the square on its radius is pi. Thus, pi is a ratio of plane figures even though it is not a ratio of lines. Ratios of more than two terms Throughout Book V the only ratios that are considered are those with two terms in accordance with V.Def.3, but in Book VII ratios of three or more terms are used in proposition VI.33 .
G is shown.
These multiterm ratios and proportions are probably left over from an earlier time.