I shall now record the peculiarities of the 3, 4, 5 or Pythagorean triangle, and the right-angled triangle 20, 21, 29.
§ 7. PECULIARITIES OF THE TRIANGLES 3, 4, 5, AND 20, 21, 29.
The 3, 4, 5 triangle contains 36° 52′ 11·65″ and the complement or greater angle 53° 7′ 48·35″
| Radius | 5 | = | 60 | whole numbers.[6] |
| Co-sine | 4 | = | 48 | " |
| Sine | 3 | = | 36 | " |
| Versed sine | 1 | = | 12 | " |
| Co-versed sine | 2 | = | 24 | " |
| Tangent | 3¾ | = | 45 | " |
| Secant | 6¼ | = | 75 | " |
| Co-tangent | 6⅔ | = | 80 | " |
| Co-secant | 8⅓ | = | 100 | " |
Tangent + Secant = Diameter or 2 Radius
Co-tan + Co-sec = 3 Radius
Sine : Versed-sine :: 3 : 1
Co-sine : Co-versed sine :: 2 : 1
Figure 30 illustrates the preceding description. Figure 31 shows the 3·1 triangle, and the 2·1 triangle built up on the sine and co-sine of the 3, 4, 5 triangle.