Geometry: bisecting a triangle with one cut parallel to its base
A single parallel cut divides a triangle into two equal parts, proved from the science of weights
A sparse geometry folio whose upper text is headed simply 'Geometry.' Leonardo poses the task of dividing a triangle into two equal parts with a single cut made parallel to its base, and states that this is proved in the sixth proposition of the third book 'on weights' (de ponderibus). The right margin carries small figures: a triangle divided by a line parallel to the base, the same triangle divided by three parallel lines, and two, then three, concentric squares. Most of the leaf is left blank.
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Bisecting a triangle with a single parallel cut
Leonardo sets the problem of dividing a triangle into two equal parts by one cut made parallel to its base. The marginal figures show the triangle divided by one line and then by three parallel lines.
Proof drawn from the treatise on weights
The equal division is said to be proved in the sixth proposition of the third book 'de ponderibus' (on weights), linking this geometric result to Leonardo's own science of statics.