The case of the disappearing angle units, or "the dangle of the angle"

[Albert Chan]

Hi, ijabbott

I am reading Trigonometric Delights, by Eli Maor.
Chapter 4, Trigonometry becomes Analytic, page 53:

Quote:Euler and his Introductio to fully incorporate complex numbers into trigonometry: with him the subject becomes truly analytic.

These developments moved trigonometry ever farther from its original connection with a triangle.
The first to define the trigonometric functions as pure numbers, rather than ratios in a triangle ...
Today, of course, we go a step farther and define the independent variable itself as a real number rather than an angle.