en.wikipedia.org/wiki/Sine

The sine and cosine functions are related in multiple ways. ... It is possible to
express any trigonometric function in ...

mathworld.wolfram.com/Sine.html

where e is the base of the natural logarithm and i is the imaginary number. Sine
is an entire function and is implemented in the Wolfram Language as Sin[z].

www.purplemath.com/modules/grphtrig.htm

Let's start with the basic sine function, f (t) = sin(t). This function has an amplitude
of 1 because the graph goes one unit up and one unit down from the midline of ...

www.mathopenref.com/sine.html

Definition of the sine function as applied to right triangles in trigonometry.

math2.org/math/algebra/functions/sincos/

Definition 1 is the simplest and most intuitive definition of the sine and cosine
function. The sine definition basically says that, on a right triangle, the following ...

jwilson.coe.uga.edu/EMT668/EMAT6680.2003.fall/Kirkham/assign1/assignment1.html

Examining the Sine Function. (Assignment 1). by. Robin Kirkham, Cara Haskins ,
and Matt Tumlin. Let us examine the sine function as the coefficient values ...

www.khanacademy.org/math/trigonometry/unit-circle-trig-func/graphs-of-sine-cosine-tangent/v/we-graph-domain-and-range-of-sine-function

Sal draws the graph of the sine function to learn about its domain and range.

docs.scipy.org/doc/numpy-1.10.1/reference/generated/numpy.sin.html

Notes. The sine is one of the fundamental functions of trigonometry (the
mathematical study of triangles). Consider a circle of radius 1 centered on the
origin.

www.mathsisfun.com/sine-cosine-tangent.html

Sine, Cosine and Tangent are the main functions used in Trigonometry and are
based on a Right-Angled Triangle. Before getting stuck into the functions, it helps
...

betterexplained.com/articles/intuitive-understanding-of-sine-waves/

I was stuck thinking sine had to be extracted from other shapes. A quick analogy:
You: Geometry is about shapes, lines, and so on. Alien: Oh? Can you show me ...