sine is defined as:
$sin(\alpha) = \frac{opposite}{hypotenuse}$
My questions are:
- why is sine only defined on right angles?
- where does the definition comes from/is derived?
- is the unit circle used to define sine or just to show the values?
as far as I know sine is defined and derived with the idea of Similarity of Triangles but I do not understand exactly why and why these triangles have to be right angles
