Isosceles Triangles and an Extended Base
Studies of equal base angles and an obtuse exterior angle
Three pen-drawn triangles study the angles of isosceles figures: one with its two base angles marked equal by paired dots, one whose base is extended to the right to produce an obtuse exterior angle, and a plain isosceles triangle below. A short caption, 'Attached', accompanies a segment joined to another to form an angle. Only this single word is transcribed; further faint jottings and show-through from adjacent leaves are also visible on the sheet.
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Equal base angles of an isosceles triangle
The uppermost figure is an isosceles triangle whose two base angles are marked as equal by two similar dots. It establishes the equality of the angles at the base, the starting point for the extensions studied below.
A segment attached to form an angle
A short segment meets another segment to form an angle, with the word 'Attached' written below. The note flags the joining of the two lines that generates the angle under study.
Extended base and obtuse exterior angle
In a second view the triangle's base is carried outward, producing an obtuse exterior angle that is marked by a dot. The extension shows how prolonging one side opens the adjacent angle beyond a right angle.