Trong các hệ thức sau, hệ thức nào sai?              

Chọn D

A. \(\frac{{{\rm{cos2}}x}}{{1 + \sin 2x}} = \frac{{{\rm{co}}{{\rm{s}}^2}x - {{\sin }^2}x}}{{{{(\sin x + {\rm{cos}}x)}^2}}} = \frac{{{\rm{(cos}}x - \sin x)(\sin x + {\rm{cos}}x)}}{{{{(\sin x + {\rm{cos}}x)}^2}}} = \frac{{{\rm{cos}}x - \sin x}}{{\sin x + {\rm{cos}}x}} = \frac{{1 - \tan x}}{{1 + \tan x}}\).

B. \(4\sin a.\cos a{\rm{(1 - 2si}}{{\rm{n}}^2}a{\rm{) = }}2\sin 2a.{\rm{cos2}}a{\rm{ = }}\sin 4a\).

C. \({\rm{cos 4}}a{\rm{  = 2}}{\cos ^2}2a - 1{\rm{ =  2(2}}{\cos ^2}a - 1{)^2}{\rm{ = 8cos}}{{\rm{ }}^4}a - 8{\cos ^2}a + 1\).

D. \[{\rm{cos 4}}a{\rm{  -  4cos }}2a + 3 = 2{(1 - 2{\sin ^2}a)^2} - 1 - 4(1 - 2{\sin ^2}a) + 3 = 8{\sin ^4}a\]\(\).