Xét cung $\alpha$ là cho $\frac{tan^2\alpha-sin^2\alpha }{cot^2\alpha -cos^2\alpha }$ có nghĩa. Khi đó $\frac{tan^2\alpha-sin^2\alpha }{cot^2\alpha -cos^2\alpha }=\frac{tan^2\alpha-\frac{tan^2\alpha }{tan^2\alpha +1}}{\frac{1}{tan^2\alpha } -\frac{1}{tan^2\alpha +1} }=tan^6\alpha $.
Xét cung $\alpha$ là
m cho $\frac{tan^2\alpha-sin^2\alpha }{cot^2\alpha -cos^2\alpha }$ có nghĩa. Khi đó $\frac{tan^2\alpha-sin^2\alpha }{cot^2\alpha -cos^2\alpha }=\frac{tan^2\alpha-\frac{tan^2\alpha }{tan^2\alpha +1}}{\frac{1}{tan^2\alpha } -\frac{1}{tan^2\alpha +1} }=tan^6\alpha $.