الدوال المثلثية

ليكن x عددا حقيقيا و k عددا صحيحا نسبيا
Cos(x+2π)=cos x
Cos(x+2kπ)=cos x
Cos(-x)=cos x
Cos(π/2 – x)=sin x
Cos(π/2 + x)=-sin x
Cos(π-x)=-cos x
Sin(π-x)= sin x

Sin(x+2 sinπ)=sin x
Sin(x+2kπ)=sin x
Sin(-x)=-sin x
Sin(π/2 – x)=cos x
Sin(π/2 + x)= cos x
Sin (π-x)= sin x
Sin(π+x)=-sin x

Tan(x+π)=tan x
Tan(x+kπ)=tan x
Tan(-x)=-tan x
Tan(π/2 – x)=1/tan x
Tan(π/2 + x)=-1/tan x
Tan(π-x)=-tan x
Tan(π+x)=tan x