Classification of triangles by angle and side
Third lesson: acute, right and obtuse triangles and their forms
Folio 1r opens the notebook's geometry with a classification of triangles. The text distinguishes three kinds by their angles - acute, right (orthogonal) and obtuse - then subdivides them by their sides into equilateral, isosceles and scalene. Two rows of triangle figures illustrate each class, with Italian captions written beneath them.
On this page
Three kinds of triangle by their angles
Triangles are of three sorts: the first has three acute angles, the second one right and two acute, and the third one obtuse and two acute. The three are drawn in series and labelled equilateral, right triangle and obtuse triangle.
Forms of the acute triangle
The triangle with three acute angles can take three forms: with three equal sides, with two equal sides, or with three unequal sides. A second row of triangles shows the equilateral, isosceles and scalene cases.
The right triangle in two sorts
The right triangle is of two kinds only: one with two equal sides, the other with three unequal sides. Two right triangles of the same height close the page, the second given a longer base.