Ta có:$M=\frac{(\tan^{2} x+1)^3-\tan^{4} x(\tan^{2} x+1)-(\tan^{2} x+1)}{(\tan^{2} x+1)^3-\tan^{6} x-1}.\frac{\tan x+1}{\tan x-1}= -\frac{14}{3}.$
Ta có:$M=\frac{(\tan^{2} x+1)^3-\tan^{4} x(\tan^{2} x+1)-1}{(\tan^{2} x+1)^3-\tan^{6} x-1}.\frac{\tan x+1}{\tan x-1}= -\frac{154}{25}.$
Ta có:$M=\frac{(\tan^{2} x+1)^3-\tan^{4} x(\tan^{2} x+1)-
(\tan^{2} x+1
)}{(\tan^{2} x+1)^3-\tan^{6} x-1}.\frac{\tan x+1}{\tan x-1}= -\frac{14}{
3}.$