What's the use of subtangent and subnormal lines?

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In summary, the subtangent and subnormal lines are obsolete concepts that have been replaced by the use of trigonometric functions to describe tangent lines. Wikipedia states that they have no practical applications and have fallen out of use since the early 20th century.
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logan3
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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
 
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logan3 said:
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:
$$\cos\phi = \frac{\text{subtangent}}{\text{tangent}}\\ \sin\phi = \frac{\text{subnormal}}{\text{tangent}}$$
 

FAQ: What's the use of subtangent and subnormal lines?

1. What is the definition of subtangent and subnormal lines?

Subtangent and subnormal lines are two types of lines that are used in calculus to approximate the slope and curvature of a curve at a given point.

2. How are subtangent and subnormal lines calculated?

The subtangent is calculated by drawing a tangent line at the given point on the curve and then drawing a line perpendicular to it that intersects the x-axis. The subnormal is calculated by drawing a line perpendicular to the tangent line that intersects the y-axis.

3. What is the significance of subtangent and subnormal lines in calculus?

Subtangent and subnormal lines help us to approximate the slope and curvature of a curve at a given point, which is important in understanding the behavior of functions and solving real-world problems in various fields such as physics, engineering, and economics.

4. Are subtangent and subnormal lines always accurate?

No, subtangent and subnormal lines are only approximations of the actual slope and curvature of a curve at a given point. The accuracy of these lines depends on the smoothness of the curve and the distance of the point from the curve's inflection points.

5. Can subtangent and subnormal lines be used for any type of curve?

Yes, subtangent and subnormal lines can be used for any type of curve, as long as the curve is differentiable at the given point. However, for more complex curves, other methods may be needed to accurately estimate the slope and curvature.

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