usually referred as the function COS
Richard C. Buck has written: 'A manual of trigonometry' -- subject(s): Trigonometry 'A manual of algebra'
C. E. Goodson has written: 'Technical algebra with applications' -- subject(s): Algebra 'Technical trigonometry with applications' -- subject(s): Trigonometry
Ralph C. Steinlage has written: 'College algebra and trigonometry' -- subject(s): Algebra, Trigonometry 'S.G. College Algebra' 'SM Coll Alg & Trig' 'College algebra' -- subject(s): Algebra
They correspond to the six possible ratios of two sides of a right triangle: a/b, a/c, b/a, b/c, c/a & c/b.
plane trigonometry spherical trigonometry
The main kinds are plane trigonometry and solid trigonometry. The latter will include trigonometry in hyper-spaces.
One major contribution was that of the Pythagorean Theorem. a^2 + b^2 = c^2
It is a number - in trigonometry or elsewhere.
TRIGONOMETRY
Hipparchus is the father of trigonometry.
Trigonometry is applied in construction and building, as trigonometry measures right angled triangles.
Plane trigonometry is trigonometry carried out in (on) a plane. This could be contrasted with spherical trigonometry, which is trigonometry carried out on the surface of a sphere. Certainly there are some other more complex forms of trig.