MHB What's the use of subtangent and subnormal lines?

[logan3]

What would be the point of knowing information about the subtangent and subnormal lines? Do they have any worthwhile real-world applications? Wikipedia says that they are archaic and fell into disuse after the early 20th century.

Thank-you

 

[I like Serena]

What would be the point of knowing information about the subtangent and subnormal lines? Do they have any worthwhile real-world applications? Wikipedia says that they are archaic and fell into disuse after the early 20th century.

Thank-you

Hi logan3! :)

First time I see them and I'm not aware of any case where we may want to use them.
Instead it makes more sense to use the cosine respectively the sine to describe the tangent line.
The relation is:
$$\cos\phi = \frac{\text{subtangent}}{\text{tangent}}\\ \sin\phi = \frac{\text{subnormal}}{\text{tangent}}$$