cos²(x) + sin²(x)= 1
tan(x)= sin(x)/cos(x)
cos(a+b)= cos(a)cos(b)-sin(a)sin(b)
cos(a-b)= cos(a)cos(b)+sin(a)sin(b)
sin(a+b)= sin(a)cos(b)+sin(b)cos(a)
sin(a-b)= sin(a)cos(b)-sin(b)cos(a)