Why does the tangent function behave like the angle itself on a unit circle?

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Discussion Overview

The discussion centers around the behavior of the tangent function in relation to small angles on the unit circle, specifically exploring why the approximation \(\tan \alpha \approx \alpha\) holds true from a geometric perspective. Participants seek an intuitive understanding rather than a formal mathematical explanation.

Discussion Character

  • Exploratory
  • Conceptual clarification

Main Points Raised

  • One participant asks for an intuitive geometric explanation for why \(\tan \alpha\) can be approximated by \(\alpha\) for small angles.
  • Another participant explains that this approximation is valid because the slope of the tangent at \(\alpha=0\) leads to a situation where the length along the tangent and the arclength of the circle become nearly equal when the radius is much larger than the arclength.
  • A further comment relates this approximation to the behavior of sine and cosine functions, suggesting that for small angles, \(\sin A \approx A\) and \(\cos A \approx 1\), emphasizing the geometric interpretation of trigonometric functions as lengths on the unit circle.

Areas of Agreement / Disagreement

Participants generally agree on the validity of the approximation for small angles but do not delve into any disagreements or competing views regarding the explanation provided.

Contextual Notes

The discussion does not address potential limitations of the approximation or the conditions under which it holds, such as the specific range of angles considered small.

Who May Find This Useful

This discussion may be useful for individuals interested in the geometric interpretation of trigonometric functions, particularly in the context of small angle approximations in mathematics and physics.

member 428835
hey all

can anyone explain why, for small [itex]\alpha[/itex] we may allow [itex]\tan \alpha = \alpha[/itex] at an intuitive, geometrical perspective. i already understand the series explanation and higher order of tangent. I am just trying for a picture.

thanks!
 
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Because it is a very good approximation.

To see why: what is the slope of the tangent at ##\alpha=0##?More exactly - look at the definition of a tangent:

The length along the tangent to a circle radius R inside the some angle ##\alpha## is ##t=R\tan\alpha##
The arclength of a circle inside the same angle ##\alpha## is ##s=R\alpha##

When R>>s, then someone standing on the surface thinks the circle is actually flat.
i.e. it looks to be the same distance as the flat tangent measure. So ##t\approx s##
 
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PF for the win! thanks simon
 
Cool!

By the same token:
sinA = A
cosA = 1

When you realize that the trig functions are the names of lengths defined on a unit circle the whole thing makes a lot more sense.
 

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