[latex] \frac{1-2cos a sin a}{1-sin^2 2a} [/latex]

[latex] \frac{1-2cos \alpha *sin \alpha }{1-sin^2\alpha} \\ \frac{sin^2 \alpha -2cos \alpha *sin \alpha +cos^2 \alpha }{cos^2\alpha} \\ tg^2 \alpha -2tg \alpha +1 [/latex]