Question

1;tính A= \(\dfrac{1}{\cos290^o}+\dfrac{1}{\sqrt{3}\sin250^o}\)

2; tính B = (1+tan 20^o) ( 1+tan25^o)

3; tính tan9^o-tan27^o-tan63^o+ tan81^o

4; tính D= \(\sin^2\dfrac{\pi}{9}+\sin^2\dfrac{2\pi}{9}+\sin\dfrac{\pi}{9}\sin\dfrac{2\pi}{9}\)

5; tính E;= \(\sin\dfrac{\pi}{32}\cos\dfrac{\pi}{32}\cos\dfrac{\pi}{16}\cos\dfrac{\pi}{8}\)