Where to find it:

NodeGraph / Right Mouse Click / Add Nodes / Math / Extension Pack / C /

cos returns the trigonometric cosine of angle.

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/cos.xhtml

•Angle

Specify the quantity, in radians, of which to return the cosine.

•Output RGB

Separate computation for Input Channels Red, Green, Blue with an Alpha Channel of 1.0

•R

Computation for Input Red channel only, saved into R, G and B channel with an Alpha of 1.0

•G

Computation for Input Green channel only, saved into R, G and B channel with an Alpha of 1.0

•B

Computation for Input Blue channel only, saved into R, G and B channel with an Alpha of 1.0

•A

Computation for Input Alpha channel only, saved into R, G and B channel with an Alpha of 1.0