equal, and therefore a a f e is square, since a a is of the same length as a f , both being 1 inch. There are also four rows of these squares, with six squares in each row; that is, there are 6 × 4, or 24 squares altogether. Each of these squares has its sides 1 inch in length, and is what was called in (215) a square inch . By the same reasoning, if one side had contained 6 yards , and the other 4 yards , the surface would have contained 6 × 4 square yards ; and so on.
- Let us now suppose that the sides of a b c d, instead of being a whole number of inches, contain some inches and a fraction. For example, let a b be 3½ inches, or (114) ⁷/₂ of an inch, and let a c contain 2½ inches, or ⁹/₄ of an inch. Draw a e twice as long as a b, and a f four times as long as a c, and complete the rectangle a e f g. The rest of the figure needs no description.