Adding Two Rectangles into a Single Square
Reduce each to a square, then combine them by the penultimate of Book I
A brief geometrical note poses the problem of adding two rectangles together into a single square figure and asks how large the side of that square will be. Leonardo directs that each rectangle first be reduced to a square (with the help of the fifth proposition of this book) and then that all the squares be combined into one (by the penultimate proposition of the first book). The leaf is otherwise nearly blank, with only these few lines of text at the top.
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Combining two rectangles into one square
To add two rectangles into a square and find its side, reduce each rectangle to a square figure by the fifth proposition of this book, then reduce all the squares into a single square by the penultimate proposition of the first book.