X-\tan x=\frac{\
COS
x}{\
SIN
x}-\frac{\sin x}{\cos x}=\frac{{{\cos }^{
2
}}x-{{\sin }^{2}}x}{\sin x\,\cos x}\] \[=\frac{2\,\cos \,
2X
}{\sin \,2x}=2\,\,\cot \,\,2x.\]