the.com/cosine
the function that quietly runs your music, your maps, and your phone's every dream
means In trigonometry, the cosine of an angle is the ratio of the adjacent side to the hypotenuse in a right triangle — equivalently, the x-coordinate of a point traveling around the unit circle.
from It's literally the "co-" of sine — short for the Latin complementi sinus, "sine of the complement," because the cosine of an angle equals the sine of its complementary angle. The "sine" half has a wonderfully tangled history: Sanskrit mathematicians called the half-chord jya (later jiva); Arabic translators borrowed it as jiba, written without vowels as jb; a Latin translator misread jb as jaib, the Arabic word for "bay" or "fold," and rendered it sinus — Latin for a fold, bay, or the curve of a garment. So the name carries an ancient mistranslation, with "co-" politely tacked on the front.
- ancient roots
- Indian astronomers tabulated it 1,500 years ago
- name mishap
- sine comes from a Latin mistranslation of fold
- sound itself
- every audio file decomposes into cosine waves
- dot product
- measures the angle between any two vectors
- never tired
- oscillates forever between negative one and one
cosine similarity — metric used in machine learning to measure angle between vectors, fundamental to recommendation systems like netflix's algorithm
law of cosines — theorem relating sides and angles of triangles, used in gps triangulation and navigation systems