(追記) (追記ここまで)
cosine
cos
The trig function cosine, which is written cos θ. For acute angles, cos θ can be found by the SOHCAHTOA definition, shown below on the left. The circle definition, a generalization of SOHCAHTOA, is shown below on the right. f(x) = cos x is a periodic function with period 2π.
See also