cem⁡(z,q)=cos⁡m⁢z-q4⁢(1m+1⁢cos⁡(m+2)⁢z-1m-1⁢cos⁡(m-2)⁢z)+q232⁢(1(m+1)⁢(m+2)⁢cos⁡(m+4)⁢z+1(m-1)⁢(m-2)⁢cos⁡(m-4)⁢z-2⁢(m2+1)(m2-1)2⁢cos⁡m⁢z)+⋯.