2. Solve the equation $\cos ^{2} x \cdot \operatorname{tg}^{4} 2 x-\cos ^{2} x-\operatorname{tg}^{4} 2 x+4 \cos x \cdot \operatorname{tg}^{2} 2 x+1=0$.
Answer: $\quad x=\frac{\pi}{3}+\frac{2 \pi}{3} k, k \in Z ; \quad x=\frac{\pi}{5}+\frac{2 \pi}{5} n, n \in Z ; \quad x=2 \pi m, m \in Z$.