Re: Trigonometry is not about triangles...
If trigonometry really were about circles, then why the "tri"?
I will agree with you, though, that there's a surprisingly strong connection between circles and triangles. Thus if you were to plot a graph of the Pythagoream Theorem (x^2 + y^2 = z^2), you get a perfect circle of radius z.
PS. Interestingly, if you generalize the equation to x^n + y^n = z^n and plot their graphs for greater values of n, you find the graph morphs from a circle to a square as n approaches infinity.