That’s why the unit circle definitions of trig functions are better. “The y coordinate of the point on a unit circle 90 degrees anticlockwise from the positive x-axis” makes a lot more sense than “The ratio between the lengths of a line segment and… another identical line segment in exactly the same place”.
A right triangle indistinguishable from a line segment. In my book, that borders on blasphemy.
That’s why the unit circle definitions of trig functions are better. “The y coordinate of the point on a unit circle 90 degrees anticlockwise from the positive x-axis” makes a lot more sense than “The ratio between the lengths of a line segment and… another identical line segment in exactly the same place”.