Cos2a (1+ tg^2a)-1
УПРОСТИТЬ

[tex]cos 2\alpha(1+tg^2\alpha)-1= \frac{cos2 \alpha }{cos^2\alpha}-1= \frac{cos^2\alpha-sin^2 \alpha -cos^2 \alpha }{cos^2 \alpha }= -\frac{sin^2 \alpha }{cos^2 \alpha }=\\=-tg^2 \alpha [/tex]