If $$A+B+C=\pi, \cos B=\cos A \cos C$$, then $$\tan A \tan C=$$

The value of $$\tan \left(\frac{7 \pi}{8}\right)$$ is

$$1+\sec ^2 x \sin ^2 x=$$

If the identity $$\cos ^4 \theta=a \cos 4 \theta+b \cos 2 \theta+c$$ holds for some $$a, b, c \in Q$$ then $$(a, b, c)=$$